s Predict the output or error(s) for the following: 1.    void main() {             int  const * p=5;         ... Read More

Predict the output or error(s) for the following: 1.     struct aaa{ struct aaa *prev; int i; struct aaa *next; }; main() {  struct aaa abc,def,ghi,jkl;  int x=100;  abc.i=0;abc.prev=... Read More

1. what is the diffrence between gross profit& net proffit?         capitaliq what is the journal?               ... Read More

What does static variable mean? What is a pointer? What is a structure? What are the differences between structures and arrays? In header files whether functions... Read More

In C, we can supply arguments to ’main’ function. The arguments that we pass to main ( ) at command prompt are called command line arguments. These arguments are supplied at the time of invoking the program. The main ( ) function... Read More

2. main() { char s[ ]="man"; int i; for(i=0;s[ i ];i++) printf("n%c%c%c%c",s[ i ],*(s+i),*(i+s),i[s]); } Answer: mmmm aaaa nnnn Explanation: s[i], *(i+s), *(s+i), i[s] are all different ways of expressing the same idea. Generally array... Read More

Programming in C _ A Tutorial Brian W. Kernighan Bell Laboratories, Murray Hill, N. J. 1. Introduction. C is a computer language available on the GCOS and UNIX operating systems at Murray Hill and (in preliminary form) on OS/360 at Holmdel. C lets... Read More

for loop: When it is desired to do initialization, condition check and increment/ decrement in a single statement of an iterative loop, it is recommended to use ’for’ loop. Syntax: for(initialisation;condition;increment/decrement) { /... Read More

1. Automatic storage class:   Storage : main memory.   Default value : garbage value.   Scope : local to the block in which the variable is defined.   Lifetime : till control remains... Read More

C interview questions and answers What will print out? main() {         char *p1=“name”;         char *p2;      ... Read More

Example: Suppose in byte that has a value 10101101 . We wish to check whether   bit number 3 is ON (1) or OFF (0) . Since we want to check the bit number 3, the second operand for AND operation we choose is binary 00001000,... Read More

      Precise answers to these and many similar questions depend of       course on the processor and compiler in use.  If you simply must       know, you’ll... Read More

      At the present time, there is little difference.  The C Standard       says that enumerations may be freely intermixed with other       integral types,... Read More

      The equivalence between arrays and pointers     allows a pointer       to malloc’ed memory to simulate an array       quite effectively.... Read More

      There is a special "short-circuiting" exception for those       operators.  The right-hand side is not evaluated if the left-       hand side determines the... Read More

I can’t seem to define a linked list successfully.  I tried               typedef struct {          ... Read More

      When the term "null" or "NULL" is casually used, one of several       things may be meant:         1.    The conceptual null pointer, the... Read More

      All of these questions are outside of the scope of this list and       have much more to do with the networking facilities which you       have available than they do... Read More

      Yes, Virginia, array subscripting is commutative in C.  This       curious fact follows from the pointer definition of array       subscripting, namely that a[e]... Read More

      The usual goal is to write a macro that can be invoked as if it       were a statement consisting of a single function call.  This       means that the "caller"... Read More

C has three types of storage: automatic, static and allocated. Variable having block scope and without static specifier have automatic storage duration. Variables with block scope, and with static specifier have static scope. Global... Read More

      Since the absolute accuracy of floating point values varies, by       definition, with their magnitude, the best way of comparing two       floating point values is to... Read More

      The definitive grammar is of course the one in the ANSI       standard;.  Another grammar (along with       one for C++) by Jim Roskind is in pub/c++grammar1.1... Read More

1. calloc(...) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size). malloc(...) takes in only a single argument... Read More

Macro gets to see the Compilation environment, so it can expand __ __TIME__ __FILE__ #defines. It is expanded by the preprocessor. For example, you can’t do this without macros #define PRINT(EXPR) printf( #EXPR “=%d... Read More

Encapsulation is binding of attributes and behaviors. Hiding the actual implementation and exposing the functionality of any object. Encapsulation is the first step towards OOPS, is the procedure of covering up of data and functions into a... Read More

Allocation of memory at the time of execution is called dynamic memory allocation. It is done using the standard library functions malloc() and calloc(). It is defined in "stdlib.h". malloc(): used to allocate required number of bytes in... Read More

Union is a collection of data items of different data types. It can hold data of only one member at a time though it has members of different data types. If a union has two members of different data types, they are allocated the same memory.... Read More

Program: #include<stdio.h> main() { int i = 65; int k = 120; printf(" value of i=%d k=%d before swapping", i, k); i = i ^ k; k = i ^ k; i = i ^ k; printf(" value of i=%d k=%d after swapping", i, k); } Explanation: i = 65; binary equivalent of... Read More

      Not at all.  (What you heard has to do with formal parameters to       functions;)  Arrays are not pointers.  The       array declaration char a[6]... Read More

      There’s no standard way, although it is a common need.  gcc       provides a -dM option which works with -E, and other compilers       may provide something... Read More

      There are far too many books on C to list here; it’s impossible       to rate them all.  Many people believe that the best one was       also the first:... Read More

      As of this writing, C has no way of generating anonymous       structure values.  You will have to use a temporary structure       variable or a little structure... Read More

      Once upon a time, Unix had a fairly nice little set of device-       independent plot functions described in plot(3) and plot(5).       The GNU libplot package... Read More

If a number, which when read in both forward and backward way is same, then such a number is called a palindrome number. Program: #include<stdio.h> main() { int n, n1, rev = 0, rem; printf("Enter any number: ... Read More

1. void main() { int const * p=5; printf("%d",++(*p)); } Answer: Compiler error: Cannot modify a constant value. Explanation: p is a pointer to a "constant integer". But we tried to change the value of the "constant integer". Read More

1.31: This code, straight out of a book, isn’t compiling: Read More

Q :  What’s the difference between these two declarations?               struct x1 { ... };            ... Read More

      Not in general.         Operator precedence and explicit parentheses impose only a       partial ordering on the evaluation of an expression.  In the ... Read More

Q:    I have a char * pointer that happens to point to some ints, and Read More

Q:    If NULL were defined as follows:               #define NULL ((char *)0)   ... Read More

      That’s a pretty misleading question.  When you declare       a pointer variable, as in               char *p;  ... Read More

      Unfortunately, no.  You may have to keep sets of preprocessor       macros (e.g. MY_TYPE_DEFINED) recording whether certain typedefs         ... Read More

Q:  Why does this code: Read More

      Alas, there is no standard or portable way to do these things in       C.  Concepts such as screens and keyboards are not even       mentioned in the Standard,... Read More

      A reasonable computer ought to give you transparent access to       all available memory.  If you’re not so lucky, you’ll either       have to rethink... Read More

      The answer is entirely dependent on the machine and the specific       calling sequences of the various compilers in use, and may not       be possible at all. ... Read More

In const char* p, the character pointed by ‘p’ is constant, so u cant change the value of character pointed by p but u can make ‘p’ refer to some other location. in char const* p, the ptr ‘p’ is constant not... Read More

Bitwise AND operator (&), one’s complement operator(~) Example: To unset the 4th bit of byte_data or to turn off a particular bit in a   number. Explanation: consider, char byte_data= 0b00010111; byte_data= ... Read More

Swapping interchanges the values of two given variables. Logic: step1: x=x+y; step2: y=x-y; step3: x=x-y; Example: if x=7 and y=4 step1: x=7+4=11; step2: y=11-4=7; step3: x=11-7=4; Thus the values of the variables x and y are interchanged... Read More

Left shifting of an unsigned integer is equivalent to multiplying an unsigned int by 2. Eg1: 14<<1; consider a number 14-----00001110 (8+4+2)is its binary equivalent left shift it by 1--------------00011100(16+8+4) which is 28. Eg2: 1<<1;... Read More

Q:    My compiler is leaving holes in structures, which is wasting Read More

      Many programmers believe that NULL should be used in all pointer       contexts, as a reminder that the value is to be thought of as a       pointer.  Others feel... Read More

      Here are two simple rules you can follow:         1.    When you want a null pointer constant in source code,           ... Read More

      Be sure to call fseek before you write, both to seek back to the       beginning of the string you’re trying to overwrite, and because       an fseek or fflush... Read More

      Just use the time(), ctime(), localtime() and/or strftime()       functions.  Here is a simple example:               ... Read More

Q:   I had a frustrating problem which turned out to be caused by the Read More

Q:      I have a varargs function which accepts a float parameter.  Why Read More

      printf() does return a value, though few programs bother to       check the return values from each call.  Since some compilers       (and lint) will warn about... Read More

Static memory allocation: The compiler allocates the required memory space for a declared variable.By using the address of operator,the reserved address is obtained and this address may be assigned to a pointer variable.Since most of the declared... Read More

Constructor with no arguments or all the arguments has default values. In Above Question Test() is a default constructor Read More

Program: #include<stdio.h> main() { int a[10]; int i; int greatest; printf("Enter ten values:"); //Store 10 numbers in an array for (i = 0; i < 10; i++) { scanf("%d", &a[i]); } //Assume that a[0] is greatest greatest = a[0]; ... Read More

Variable length argument lists Read More

      Uninitialized variables with "static" duration (that is, those       declared outside of functions, and those declared with the       storage class static), are... Read More

1.32: What is the difference between these initializations? Read More

Q:    I have a function which accepts, and is supposed to initialize, Read More

      Have you #included <stdlib.h>, or otherwise arranged for            malloc() to be declared properly? Read More

      Some pre-ANSI compilers/preprocessors interpreted macro       definitions like               #define TRACE(var, fmt) printf(... Read More

      The #pragma directive provides a single, well-defined "escape       hatch" which can be used for all sorts of (nonportable)       implementation-specific controls... Read More

      Here is one method, recommended by Knuth and due originally to       Marsaglia:               #include <stdlib.h>  ... Read More

      It is straightforward to define a simple structure and some       arithmetic functions to manipulate them.  C9X will support          ... Read More

      There’s an older header, <varargs.h>, which offers about the            same functionality. Read More

      The contest is in a state of flux; see       http://www.ioccc.org/index.html for current details.         Contest winners are usually announced at a Usenix... Read More

Create two pointers, and set both to the start of the list. Update each as follows: while (pointer1) { pointer1 = pointer1->next; pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next; if (pointer1 == pointer2) { print (... Read More

there are 3 main uses for the static. 1. If you declare within a function: It retains the value between function calls 2.If it is declared for a function name: By default function is extern..so it will be visible from other files if the... Read More

To hash means to grind up, and that’s essentially what hashing is all about. The heart of a hashing algorithm is a hash function that takes your nice, neat data and grinds it into some random-looking integer. The idea behind hashing is... Read More

Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the... Read More

There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void*... Read More

A static function is a function whose scope is limited to the current source file. Scope refers to the visibility of a function or variable. If the function or variable is visible outside of the current source file, it is said to have global, or... Read More

Register variables are stored in the CPU registers. Its default value is a garbage value. Scope of a register variable is local to the block in which it is defined. Lifetime is till control remains within the block in which the register... Read More

A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 5, 7,… are prime numbers. Program: #include <stdio.h>main() { int n, i, c = 0;     printf("Enter... Read More

Swapping interchanges the values of two given variables. Logic: step1: temp=x; step2: x=y; step3: y=temp; Example if x=5 and y=8, consider a temporary variable temp. step1: temp=x=5; step2: x=y=8; step3: y=temp=5; Thus the values of the variables x... Read More

3. main() { float me = 1.1; double you = 1.1; if(me==you) printf("I love U"); else printf("I hate U"); } Answer: I hate U 2 Explanation: For floating point numbers (float, double, long double) the values cannot be predicted exactly. Depending on the... Read More

      As a matter of style, many programmers prefer not to have       unadorned 0’s scattered through their programs.  Therefore, the       preprocessor macro... Read More

Q:    I use the preprocessor macro               #define Nullptr(type) (type *)0   ... Read More

      In one source file you defind an array of characters and in the       other you declared a pointer to characters.  The declaration       extern char *a simply... Read More

      The type.         In Standard C, &arr yields a pointer, of type pointer-to-array-       of-T, to the entire array.  (In pre-ANSI C, the & in &... Read More

      Yes.  Remember that a pointer is different from what it points       to.  Local variables are deallocated when the function returns,       but in the case of... Read More

      Most implementations of malloc/free do not return freed memory       to the operating system, but merely make it available for future       malloc() calls within the... Read More

Unfortunately, there is no standard or portable way. Read More

      The <> syntax is typically used with Standard or system-supplied       headers, while "" is typically used for a program’s own header       ... Read More

      You can’t do it directly; preprocessor #if arithmetic uses only       integers.  An alternative is to #define several macros with       symbolic names... Read More

      No.  Preprocessing happens during an earlier phase of       compilation, before type names have been parsed.  Instead of       sizeof, consider using the... Read More

      You probably can’t.  (Preprocessor arithmetic uses only long       integers, and there is no concept of addressing.)  Are you       sure you need... Read More

      Doing so is legal, but requires a certain amount of care.  Modern practice,       however, is to       use the prototyped form in both declarations and definitions. ... Read More

      Under ANSI C, the text inside a "turned off" #if, #ifdef, or       #ifndef must still consist of "valid preprocessing tokens."       This means that the characters... Read More

      It is an extension implemented by some preprocessors to help       make header files idempotent; it is equivalent to the #ifndef          ... Read More

      A compiler may do anything it likes when faced with undefined       behavior (and, within limits, with implementation-defined and       unspecified behavior),... Read More

      The arguments you pass to scanf() must always be pointers.            To fix the fragment above, change it to scanf("%d", &i) . Read More

      scanf() has a number of problems --         More generally, scanf() is designed for relatively structured,       formatted input (its name is in fact derived... Read More

      Unlike fgets(), gets() cannot be told the size of the buffer       it’s to read into, so it cannot be prevented from overflowing          ... Read More

      By "array of strings" you probably mean "array of pointers to       char."  The arguments to qsort’s comparison function are       pointers to the objects... Read More

      That message is a quirk of the old Unix linkers.  You get an       error about _end being undefined only when other symbols are       undefined, too -- fix the... Read More

      So that a proper prototype for printf() will be in scope.         A compiler may use a different calling sequence for functions       which accept... Read More

       Bob Stout’s popular "SNIPPETS" collection is available from       ftp.brokersys.com in directory pub/snippets or on the web at       http://www.brokersys... Read More

Q:      Why can’t I open a file by its explicit path?  The call Read More

      You want a dynamic linker or loader.  It may be possible to       malloc some space and read in object files, but you have to know       an awful lot about object... Read More

Q:     Is C a great language, or what?  Where else could you write       something like a+++++b ?   A:    Well, you can’t meaningfully write... Read More

      C++ was derived from C, and is largely based on it, but there       are some legal C constructs which are not legal C++.       Conversely, ANSI C inherited several... Read More

      Use mktime() or localtime()   beware of DST adjustments if tm_hour       is 0), or Zeller’s       congruence (see the sci.math FAQ list), or this... Read More

#include main() { typedef union { int a; char b[10]; float c; } Union; Union x,y = {100}; x.a = 50; strcpy(x.b,"hello"); x.c = 21.50; printf("Union x : %d %s %f n",x.a,x.b,x.c); printf("Union y : %d %s %f n",y.a,y.b,y.c);... Read More

A major difference is: string will have static storage duration, whereas as a character array will not, unless it is explicity specified by using the static keyword. Actually, a string is a character array with following properties: * the... Read More

If a program is large, it is subdivided into a number of smaller programs that are called modules or subprograms. If a complex problem is solved using more modules, this approach is known as modular programming. Read More

Declaring a variable means describing its type to the compiler but not allocating any space for it. Defining a variable means declaring it and also allocating space to hold the variable. You can also initialize a variable at the time it is defined. ... Read More

An argument is an entity used to pass the data from calling function to the called function. Formal arguments are the arguments available in the function definition. They are preceded by their own data types. Actual arguments are available in the... Read More

Advantages of external storage class 1)Persistent storage of a variable retains the latest value 2)The value is globally available Disadvantages of external storage class 1)The storage for an external variable exists even when the variable is... Read More

A pointer variable is a variable that may contain the address of another variable or any valid address in the memory. Read More

As the name suggests, the function acts as a friend to a class. As a friend of a class, it can access its private and protected members. A friend function is not a member of the class. But it must be listed in the class definition. Read More

A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero. class Shape { public: virtual... Read More

Register variables: belong to the register storage class and are stored in the CPU   registers. The scope of the register variables is local to the block in which the variables are defined. The variables which are used for... Read More

Program: #include<stdio.h>   main() {   int a, b, c;   printf("Enter a,b,c: ... Read More

It can be used as a stylistic hint to indicate that the       function’s definition is probably in another source file, but       there is no formal difference between ... Read More

      One good way is for clients to use structure pointers (perhaps       additionally hidden behind typedefs) which point to structure       types which are not... Read More

Q:    So given               a[i] = i++;         we don... Read More

      Since the two forms differ only in the value yielded, they are       entirely equivalent when only their side effect is needed.       (However, the prefix form is... Read More

There is no single perfect method.  Given the declarations               int array[NROWS][NCOLUMNS];             int **array1... Read More

Q:    I see code like               char *p = malloc(strlen(s) + 1);        ... Read More

      ANSI C sanctions this usage (and the related realloc(..., 0),       which frees), although several earlier implementations do not       support it, so it may not be... Read More

      It is true (sic) that any nonzero value is considered true in C,       but this applies only "on input", i.e. where a Boolean value is       expected.  When a... Read More

      It’s a question of style, and thus receives considerable debate.       Many people believe that "nested #include files" are to be       avoided: the... Read More

      Standard headers exist in part so that definitions appropriate       to your compiler, operating system, and processor can be       supplied.  You cannot just... Read More

      No.  You can’t "run the preprocessor on itself," so to speak.       What you can do is use one of two completely separate #define       lines, depending... Read More

Q:    I inherited some code which contains far too many #ifdef’s for       my taste.  How can I preprocess the code to leave only one     ... Read More

      It doesn’t matter whether main() returns or not, or whether       anyone looks at the status; the problem is that when main() is       misdeclared, its caller ... Read More

      You can use something like the following two-step procedure to       force a macro to be expanded as well as stringized:          ... Read More

      It is legal in ANSI C (and perhaps in a few pre-ANSI systems),       though useful only in rare circumstances.  It declares an array       of size three,... Read More

      The problem is older linkers which are under the control of       neither the ANSI/ISO Standard nor the C compiler developers on       the systems which have them.... Read More

      Many compilers support a few non-Standard extensions, gcc more       so than most.  Are you sure that the code being rejected doesn’t       rely on such an... Read More

      Simply double the percent sign: %% .         % can’t work, because the backslash is the *compiler’s*       escape character, while here our... Read More

      ftell() and fseek() use type long int to represent offsets       (positions) in a file, and may therefore be limited to offsets       of about 2 billion (2**31-1).... Read More

      Make sure you recognize the difference between classic regular       expressions (variants of which are used in such Unix utilities       as ed and grep), and filename... Read More

      You can call srand() to seed the pseudo-random number generator       with a truly random initial value.  Popular seed values are the       time of day, or the... Read More

      Make sure you’re actually linking with the math library.  For       instance, under Unix, you usually need to use the -lm option, at        ... Read More

      Use vprintf(), vfprintf(), or vsprintf().         Here is an error() function which prints an error message,       preceded by the string "error: " and... Read More

      Products called PC-Lint and FlexeLint (in "shrouded source       form," for compilation on ’most any system) are available from           ... Read More

      It is actually quite difficult to write a self-reproducing       program that is truly portable, due particularly to quoting and       character set difficulties. ... Read More

Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through... Read More

Sometimes you can get away with using a small memory model in most of a given program. There might be just a few things that don’t fit in your small data and code segments. When that happens, you can use explicit far pointers and function... Read More

An lvalue is an expression to which a value can be assigned. The lvalue expression is located on the left side of an assignment statement, whereas an rvalue is located on the right side of an assignment statement. Each assignment statement must have... Read More

When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings. Examples: 1) The operators >> and << may be used for I/O operations because in the header,... Read More

A goto statement implements a local jump of program execution, and the longjmp() and setjmp() functions implement a nonlocal, or far, jump of program execution. Generally, a jump in execution of any kind should be avoided because it is not... Read More

Class is concrete representation of an entity. It represents a group of objects, which hold similar attributes and behavior. It provides Abstraction and Encapsulations. Classes are generally declared using the keyword class. Read More

Object represents/resembles a Physical/real entity. An object is simply something you can give a name. Object Oriented Programming is a Style of programming that represents a program as a system of objects and enables code-reuse. Read More

A nested class is a class enclosed within the scope of another class. For example: // Example 1: Nested class // class Outer Class {class Nested Class {// …}; //... Read More

The preprocessor is used to modify your program according to the preprocessor directives in your source code. Preprocessor directives (such as #define) give the preprocessor specific instructions on how to modify your source code. The... Read More

Overloading - Two functions having same name and return Type, but with different type and/or number of arguments. Overriding - When a function of base class is re-defined in the derived class. Read More

The concept of arrays has a block of memory reserved. The disadvantage with the concept of arrays is that the programmer must know, while programming, the size of memory to be allocated in addition to the array size remaining constant... Read More

Parameter –While defining method, variable passed in the method are   called parameters. Arguments-While using those methods value passed to those variables are   called arguments. Read More

A static variable is a special variable that is stored in the data segment unlike the default automatic variable that is stored in stack. A static variable can be initialised by using keyword static before variable name. For Example: ... Read More

Enumeration is a data type. We can create our own data type and define values that the variable can take. This can help in making program more readable. enum   definition is similar to that of a structure. Example: consider... Read More

Pointers are special variables which store address of some other variables. Syntax: datatype *ptr;     Here * indicates that ptr is a pointer variable which represents value stored at a particular address. ... Read More

Functions and macros are declared in header files. Header files would be included in source files by the compiler at the time of compilation. Header files are included in source code using #include directive.#include<some.h> includes all the... Read More

  Pointer –pointer is a variables that hold the address of another variable .It is used to manipulate   data using the address, pointer use the * operator to access the data pointed by them. Array –array use... Read More

      If you might need large values (above 32,767 or below -32,767),       use long.  Otherwise, if space is very important (i.e. if there       are... Read More

The forthcoming revision to the C Standard (C9X) specifies type       long long as effectively being at least 64 bits, and this type       has been implemented by a number of... Read More

        First, though there can be many "declarations" (and in many       translation units) of a single "global" (strictly speaking,       ... Read More

        You can’t quite do it directly.  Either have the function return       a generic function pointer, with some judicious casts to adjust    ... Read More

       Most certainly Read More

      Structures may have this padding (as well as internal padding),       if necessary, to ensure that alignment properties will be       preserved when an array of... Read More

Q:    This program works correctly, but it dumps core after it Read More

      The current C Standard allows an initializer for the first-named       member of a union.  C9X will introduce "designated initializers"       which can be used to... Read More

      No.  You can write a little function to map an enumeration       constant to a string.  (For debugging purposes, a good debugger       should automatically... Read More

      A sequence point is a point in time (at the end of the       evaluation of a full expression, or at the ||, &&, ?:, or comma       operators, or just before a... Read More

Q:    I have a complicated expression which I have to assign to one of Read More

Q:    I’m trying to declare a pointer and allocate some space for it, Read More

      Postfix ++ essentially has higher precedence than the prefix       unary operators.  Therefore, *p++ is equivalent to *(p++); it       increments p, and... Read More

      Not portably.  There is no generic pointer-to-pointer type in C.       void * acts as a generic pointer only because conversions are       applied... Read More

      The same as on any other machine: as 0 (or some version of 0;               Whenever a programmer requests a null pointer, either by writing   ... Read More

      No.  (Using NULL may be preferable, but not for this reason.)       Although symbolic constants are often used in place of numbers       because the numbers might... Read More

      If for no other reason, doing so would be ill-advised because it       would unnecessarily constrain implementations which would       otherwise naturally represent... Read More

      This message, which typically occurs with MS-DOS compilers, means       that you’ve written, via a null (perhaps because uninitialized)       pointer, to an... Read More

      This is a bit of an oversimplification.  An array name is       "constant" in that it cannot be assigned to, but an array is       *not* a pointer, as the... Read More

      Until recently, you couldn’t.  Array dimensions in C       traditionally had to be compile-time constants.  C9X will       introduce variable-length... Read More

      The returned pointer should be to a statically-allocated buffer,       or to a buffer passed in by the caller, or to memory obtained       with malloc(), but *not* to... Read More

      Before ANSI/ISO Standard C introduced the void * generic pointer       type, these casts were typically required to silence warnings       (and perhaps induce... Read More

Q:    I’m allocating a large array for some numeric work, using the Read More

      Under the segmented architecture of PC compatibles, it can be       difficult to use more than 640K with any degree of transparency,          ... Read More

      No.  Some early documentation for malloc() stated that the       contents of freed memory were "left undisturbed," but this ill-       advised guarantee was never... Read More

      When you call free(), the memory pointed to by the passed       pointer is freed, but the value of the pointer in the caller       probably remains unchanged, because... Read More

      The malloc/free implementation remembers the size of each block       as it is allocated, so it is not necessary to remind it of the       size when freeing. Read More

Q:    Why doesn’t Read More

Q:    I’m checking a string to see if it matches a particular value. Read More

Q:   If I can say Read More

      C does not provide a standard Boolean type, in part because       picking one involves a space/time tradeoff which can best be       decided by the programmer.... Read More

      The exact behavior is implementation-defined (which means that       it is supposed to be documented;.       Typically, headers named with <> syntax are searched... Read More

      One popular trick is to define and invoke the macro with a       single, parenthesized "argument" which in the macro expansion       becomes the entire argument list,... Read More

      In 1983, the American National Standards Institute (ANSI)       commissioned a committee, X3J11, to standardize the C language.       After a long, arduous process,... Read More

Q:    Why does the declaration               extern int f(struct x *p);         give me an obscure warning... Read More

      It’s a non-standard (though common) extension.  If you really       need to access the environment in ways beyond what the standard       getenv() function... Read More

      Yes and no.  The Standard says that they are equivalent.       However, a return from main() cannot be expected to work if       data local to main() might be... Read More

      The compiler doesn’t know the size of the pointed-to objects.       Before performing arithmetic, convert the pointer either to          ... Read More

      It’s possible to have a compiler available which accepts ANSI       syntax, but not to have ANSI-compatible header files or run-time       libraries installed.... Read More

      Two programs, protoize and unprotoize, convert back and forth       between prototyped and "old style" function definitions and       declarations.  (These... Read More

Q:   What’s wrong with this code? Read More

Q:    Why does the code Read More

      It’s best to use an explicit fflush(stdout) whenever output       should definitely be visible (and especially if the text does       not end with ... Read More

printf("%*d", width, x) will do just what you want. Read More

      scanf %d won’t consume a trailing newline.  If the input number       is immediately followed by a newline, that newline will       immediately satisfy the... Read More

      When scanf() is attempting to convert numbers, any non-numeric       characters it encounters terminate the conversion *and are left       on the input stream*. ... Read More

      Many implementations of the stdio package adjust their behavior       slightly if stdout is a terminal.  To make the determination,       these implementations... Read More

      fflush() is defined only for output streams.  Since its       definition of "flush" is to complete the writing of buffered       characters (not to discard them),... Read More

      There isn’t a good way.  If you need to switch back, the best       solution is not to have used freopen() in the first place.  Try       using your... Read More

      When you’re reading a binary data file, you should specify "rb"       mode when calling fopen(), to make sure that text file       translations do not occur.... Read More

      Just use sprintf().  (Don’t worry that sprintf() may be       overkill, potentially wasting run time or code space; it works       well in practice.)  ... Read More

      Older versions of toupper() and tolower() did not always work       correctly on arguments which did not need converting (i.e. on       digits or punctuation or... Read More

Q:    Now I’m trying to sort an array of structures with qsort().  My Read More

      Most computers use base 2 for floating-point numbers as well as       for integers.  In base 2, one divided by ten is an infinitely-       repeating fraction (0... Read More

      Because few processors have an exponentiation instruction.       C has a pow() function, declared in <math.h>, although explicit       multiplication is usually... Read More

      Many systems with high-quality IEEE floating-point       implementations provide facilities (e.g. predefined constants,       and functions like isnan(), either as... Read More

Q:    I’m looking for some code to do: Read More

      Use the facilities of the <stdarg.h> header.         Here is a function which concatenates an arbitrary number of       strings into malloc’ed... Read More

      C9X will support vscanf(), vfscanf(), and vsscanf().            (Until then, you may be on your own.) Read More

      Check for unclosed comments or mismatched #if/#ifdef/#ifndef/            #else/#endif directives; remember to check header files, too. Read More

      K&R, while providing the example most often copied, also supply       a good excuse for disregarding it:               The... Read More

      It’s a trick to guard against the common error of writing               if(x = 0)         If you’re in the... Read More

     Various documents are available for anonymous ftp from:               Site:             File or... Read More

      A popular and high-quality free C compiler is the FSF’s GNU C       compiler, or gcc.  It is available by anonymous ftp from       prep.ai.mit.edu in... Read More

      The problem is that traditional versions of lint do not know,       and cannot be told, that malloc() "returns a pointer to space       suitably aligned for storage of... Read More

      No.  First of all, prototypes work only if they are present and       correct; an inadvertently incorrect prototype is worse than       useless.  Secondly,... Read More

      As the number of available programs, the number of publicly       accessible archive sites, and the number of people trying to       access them all grow, this... Read More

      It’s system-dependent.  Under Unix, you typically open, read,       and write a device file in /dev, and use the facilities of the       terminal driver to... Read More

      Under Unix, either use popen()to write to       the lp or lpr program, or perhaps open a special file like       /dev/lp.  Under MS-DOS, write to the (nonstandard... Read More

      This problem is, in general, insoluble.  Under Unix, for       instance, a scan of the entire disk (perhaps involving special       permissions) would... Read More

      Either use system() to invoke your operating system’s copy       utility or open the source and destination       files (using fopen() or some lower-level file... Read More

      Your operating system may provide a routine which returns this       information, but it’s quite system-dependent. Read More

      It may or may not be possible to do so at all.  Different       operating systems implement global name/value functionality       similar to the Unix environment... Read More

      Make sure you really know what you’re asking.  Integers are       stored internally in binary, although for most purposes it is       not incorrect to think... Read More

      Was i signed or unsigned?  If it was signed, a shift is not       equivalent (hint: think about the result if i is negative and          ... Read More

      Not directly.  Sometimes, it’s appropriate to use a separate       function to map strings to integer codes, and then switch on       those.  Otherwise... Read More

      C comments don’t nest mostly because PL/I’s comments, which C’s       are borrowed from, don’t either.  Therefore, it is usually      ... Read More

      It’s not trivial to implement nested functions such that they       have the proper access to local variables in the containing       function(s), so they were... Read More

      Several freely distributable programs are available:         p2c   A Pascal to C converter written by Dave Gillespie,          ... Read More

      Yes and no, respectively.  The full expression for the present       Gregorian calendar is               year % 4 == 0 &... Read More

      It’s a devastatingly deviously unrolled byte-copying loop,       devised by Tom Duff while he was at Lucasfilm.  In its "classic"       form, it looks like:... Read More

      It was reserved to allow the possibility of having functions       with multiple, differently-named entry points, a la FORTRAN.  It       was not, to anyone&rsquo... Read More

      You can pronounce the C keyword "char" in at least three ways:       like the English words "char," "care," or "car" (or maybe even       "character"); the choice is... Read More

      An up-to-date copy may be obtained from ftp.eskimo.com in       directory u/s/scs/C-faq/.  You can also just pull it off the       net; it is normally posted to... Read More

1. When we write printf("%d",x); this means compiler will print the value of x. But as here, there is nothing after %d so compiler will show in output window garbage value. 2. When we use %d the compiler internally uses it to access the argument... Read More

sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device. Read More

Streams can be classified into two types: text streams and binary streams. Text streams are interpreted, with a maximum length of 255 characters. With text streams, carriage return/line feed combinations are translated to the newline n character and... Read More

- Pointers are used to manipulate data using the address. Pointers use * operator to access the data pointed to by them - Arrays use subscripted variables to access and manipulate data. Array variables can be equivalently written using pointer... Read More

If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable, or any other object in memory, you have an indirect reference to its value. Read More

A type cast should not be used to override a const or volatile declaration. Overriding these type modifiers can cause the program to fail to run correctly. A type cast should not be used to turn a pointer to one type of structure or data type into... Read More

A switch statement is generally best to use when you have more than two conditional expressions based on a single variable of numeric type. Read More

A Modulus operator gives the remainder value. The result of x%y is obtained by (x-(x/y)*y). This operator is applied only to integral operands and cannot be applied to float or double. Read More

A large program is subdivided into a number of smaller programs or subprograms. Each subprogram specifies one or more actions to be performed for a large program. such subprograms are functions. The function supports only static and extern storage... Read More

A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back. This approach helps the compiler ensure that calls to a function are made correctly and... Read More

’Polymorphism’ is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form.... Read More

There are two types of memory management operators in C++: · new · delete   Read More

Constructor which initializes it’s object member variables ( by shallow copying) with another object of the same class. If you don’t implement one in your class then compiler implements one for you. for example: .   ... Read More

Pass by Reference: In this method, the addresses of actual arguments in the calling   function are copied into formal arguments of the called function. This means that using these addresses, we would have an access to the... Read More

typedef declaration helps to make source code of a C program more readable. Its   purpose is to redefine the name of an existing variable type. It provides a short and meaningful way to call a data type. typedef is useful when... Read More

Main memory and CPU registers are the two memory locations where auto variables are stored. Auto variables are defined under automatic storage class. They are stored in main memory. Memory is allocated to an automatic variable when the block... Read More

#include<stdio.h>   main() {   int a;   printf("Enter a: ... Read More

In this program, user is asked for a filename he needs to change. User is also asked for the line number that is to be deleted. The filename is stored in ’filename’. The file is opened and all the data is transferred to another... Read More

Program: Program to replace a specified line in a text file. #include <stdio.h> int main(void) { FILE *fp1, *fp2; //’filename’is a 40 character string to store filename char filename[40]; char c; int del_line, temp = 1; /... Read More

Number of lines in a file can be determined by counting the number of new line characters present. Program: Program to count number of lines in a file. #include <stdio.h> int main(void) /* Ask for a filename and count number of lines in... Read More

int *(*p[10])(char *, char *); It is an array of function pointers that returns an integer pointer. Each function has two arguments which in turn are pointers to character type variable. p[0], p[1],....., p[9] are function pointers. Read more about... Read More

char *a[4]={"sridhar","raghava","shashi","srikanth"}; explain Explanation: Here a[4] is an array which holds the address of strings. Strings are character arrays themselves. Memory required to store an address is 4 bits. So memory... Read More

Nothing; it’s archaic Read More

        The first part of this question can be answered in at least       three ways:         1.  char *(*(*a[N])())();    ... Read More

        Functions which are called without a declaration in scope       (perhaps because the first call precedes the function’s      ... Read More

      Use something like               extern int func();             int (*fp)() = func;   ... Read More

Q :  I came across some code that declared a structure like this:               struct name {              ... Read More

      What K&R1 said (though this was quite some time ago by now) was       that the restrictions on structure operations would be lifted       in a forthcoming version... Read More

      It is relatively straightforward to write a structure out using       fwrite():               fwrite(&somestruct, sizeof... Read More

      ANSI C defines the offsetof() macro, which should be used if       available; see <stddef.h>.  If you don’t have it, one possible       implementation... Read More

      Build a table of names and offsets, using the offsetof() macro.       The offset of field b in struct a is               offsetb ... Read More

Q:    Why doesn’t this code: Read More

Q:   Under my compiler, the code Read More

Q:   I’ve experimented with the code Read More

Q:    Here’s a slick expression: Read More

Q:   I have a function Read More

      The language definition states that for each pointer type, there       is a special value -- the "null pointer" -- which is       distinguishable from all other... Read More

      According to the language definition, a constant 0 in a pointer       context is converted into a null pointer at compile time.  That       is, in an... Read More

      C programmers traditionally like to know more than they might       need to about the underlying machine implementation.  The fact       that null pointers are... Read More

      The Prime 50 series used segment 07777, offset 0 for the null       pointer, at least for PL/I.  Later models used segment 0, offset       0 for null pointers in... Read More

      Much of the confusion surrounding arrays and pointers in C can       be traced to a misunderstanding of this statement.  Saying that       arrays and pointers are... Read More

      It’s supposed to be a convenience.         Since arrays decay immediately into pointers, an array is never       actually passed to a function. ... Read More

     The ANSI C Standard defines a "modifiable lvalue," which an            array is not. Read More

      Usually, you don’t want to.  When people speak casually of a       pointer to an array, they usually mean a pointer to its first       element.   ... Read More

      The traditional solution is to allocate an array of pointers,       and then initialize each pointer to a dynamically-allocated       "row."  Here is a two... Read More

Q:    Here’s a neat trick: if I write Read More

      The rule by which arrays decay into pointers       is not applied recursively.  An array of arrays (i.e. a two-       dimensional array in C) decays into a... Read More

It’s not always easy.  One way is to pass in a pointer to the       [0][0] element, along with the two dimensions, and simulate       array subscripting "by hand":     ... Read More

      The compiler pretends that the array parameter was declared as a       pointer, and sizeof reports the size of the       pointer.   Read More

Q:   I just tried the code Read More

      Make sure that the pointed-to memory is properly allocated.       For example, make sure you have *not* done something like            ... Read More

      It’s hard to say.  The Standard doesn’t say that systems can act       this way, but it doesn’t explicitly say that they can’t, either. Read More

      Yes.  In general, you must arrange that each pointer returned       from malloc() be individually passed to free(), exactly once (if       it is freed at all).... Read More

      alloca() allocates memory which is automatically freed when the       function which called alloca() returns.  That is, memory       allocated with alloca is... Read More

      In C, characters are represented by small integers corresponding       to their values (in the machine’s character set), so you don’t       need a... Read More

Q:   Here are some cute preprocessor macros: Read More

      As a general rule, you should put these things in header (.h)       files:               macro definitions (preprocessor #defines... Read More

      Perhaps there’s a missing semicolon at the end of the last            declaration in the last header file you’re #including Read More

Q:    I have some old code that tries to construct identifiers with a Read More

      C’s preprocessor is not intended as a general-purpose tool.       (Note also that it is not guaranteed to be available as a       separate program.)  Rather... Read More

      Copies are available in the United States from               American National Standards Institute          ... Read More

      You can find information (including C9X drafts) at       the web sites http://www.lysator.liu.se/c/index.html,       http://www.dkuug.dk/JTC1/SC22/WG14/, and http:/... Read More

Q:    I don’t understand why I can’t use const values in initializers Read More

      "const char *p" (which can also be written "char const *p")       declares a pointer to a constant character (you can’t change       the character); "char *... Read More

      You can use a pointer-to-T (for any type T) where a pointer-to-       const-T is expected.  However, the rule (an explicit exception)       which permits slight... Read More

      Either int main(), int main(void), or int main(int argc,       char *argv[]) (with alternate spellings of argc and *argv[]       obviously allowed).  Read More

      Perhaps its author counts himself among the target audience.       Many books unaccountably use void main() in examples, and assert       that it’s correct. ... Read More

      memmove() offers guaranteed behavior if the source and       destination arguments overlap.  memcpy() makes no such       guarantee, and may therefore be more... Read More

      Perhaps it is a pre-ANSI compiler, unable to accept function            prototypes and the like. Read More

      Briefly: implementation-defined means that an implementation       must choose some behavior and document it.  Unspecified means       that an implementation... Read More

      It has always been a characteristic of C that certain constructs       behaved in whatever way a particular compiler or a particular       piece of hardware chose to... Read More

      It’s true that printf’s %f specifier works with both float and       double arguments.  Due to the "default argument promotions"       (which apply in... Read More

Q:      Why doesn’t this code: Read More

      You can’t; an asterisk in a scanf() format string means to       suppress assignment.  You may be able to use ANSI stringizing       and string... Read More

      Perhaps surprisingly, ... Read More

      When the format string being used with sprintf() is known and       relatively simple, you can sometimes predict a buffer size in an       ad-hoc way.  If the... Read More

Use freopen() Read More

      You can’t do this directly, but you could write your       own printf variant which printed everything twice. Read More

      The only Standard function available for this kind of       "tokenizing" is strtok(), although it can be tricky to use and       it may not do everything you want it... Read More

      Sometimes it’s easier to keep the list in order as you build it       (or perhaps to use a tree instead).  Algorithms like insertion       sort and merge... Read More

Q:    I know that the library function localtime() will convert a Read More

      The ANSI/ISO Standard C mktime() and difftime() functions       provide some support for both problems.  mktime() accepts non-       normalized dates, so it is... Read More

      The Standard C library has one: rand().  The implementation on       your system may not be perfect, but writing a better one isn’t       necessarily easy,... Read More

      The obvious way,               rand() % N        /* POOR */         (which tries to... Read More

      Poor pseudorandom number generators (such as the ones       unfortunately supplied with some systems) are not very random in           ... Read More

      In general, a header file contains only declarations.  In some       cases (especially if the functions are nonstandard) obtaining       the actual *definitions*... Read More

      Many linkers make one pass over the list of object files and       libraries you specify, and extract from libraries only those       modules which satisfy references... Read More

      First,       If the problem isn’t that simple, recall that digital computers       usually use floating-point formats which provide a close but by   ... Read More

      That constant (which is apparently supposed to be the value of       pi, accurate to the machine’s precision), is not standard.  If       you need pi, you... Read More

      Some compilers for small machines, including Borland’s       (and Ritchie’s original PDP-11 compiler), leave out certain       floating point support... Read More

      In the variable-length part of a variable-length argument list,       the "default argument promotions" apply: types char and       short int are promoted to int, and... Read More

      This information is not available to a portable program.  Some       old systems provided a nonstandard nargs() function, but its use       was always... Read More

Q:   My compiler isn’t letting me declare a function Read More

      The type-rewriting games which the va_arg() macro typically       plays are stymied by overly-complicated types such as pointer-to-       function.  If you use a... Read More

      In general, you cannot.  Ideally, you should provide a version       of that other function which accepts a va_list pointer       (analogous to vfprintf();). ... Read More

      There is no guaranteed or portable way to do this.  If you’re       curious, ask this list’s editor, who has a few wacky ideas you       could try... ... Read More

      Does the code look like this?               myprocedure;         C has only functions, and function calls always require ... Read More

      You probably have one or more very large (kilobyte or more)       local arrays.  Many systems have fixed-size stacks, and those       which perform dynamic... Read More

      Look for a misdeclared main() , or       local buffers passed to setbuf() or setvbuf(), or problems in            cleanup functions... Read More

      Lots of things could be going wrong; here are a few of the more       common things to check:               uninitialized local... Read More

      These generally mean that your program tried to access memory it       shouldn’t have, invariably as a result of stack corruption or       improper pointer use.... Read More

Q:   Here’s a neat trick for checking whether two strings are equal: Read More

      Hungarian Notation is a naming convention, invented by Charles       Simonyi, which encodes information about a variable’s type (and       perhaps its... Read More

      Programming style, like writing style, is somewhat of an art and       cannot be codified by inflexible rules, although discussions       about style often seem to... Read More

      A number of debugging packages exist to help track down malloc       problems; one popular one is Conor P. Cahill’s "dbmalloc",       posted to comp.sources.misc... Read More

      See if you can run lint first (perhaps with the -a, -c, -h, -p       or other options).  Many C compilers are really only half-       compilers, electing not to... Read More

      There are several of them:         Tom Torfs has a nice tutorial at       http://members.xoom.com/tomtorfs/cintro.html .       ... Read More

      One source (though not public domain) is _The Standard C       Library_, by P.J. Plauger (see the Bibliography).       Implementations of all or part of the C library... Read More

      Two possibilities are       http://www.cs.man.ac.uk/standard_c/_index.html and       http://www.dinkumware.com/htm_cl/index.html . Read More

      Two available packages are "defunc," posted to comp.sources.misc       in December, 1993 (V41 i32,33), to alt.sources in January, 1994,       and available from... Read More

      Some popular packages are the "quad" functions within the BSD       Unix libc sources (ftp.uu.net, /systems/unix/bsd-sources/..../       /src/lib/libc/quad/*), the GNU... Read More

      These, too, are entirely operating-system-specific.  Some       versions of curses have a nodelay() function.  Depending on your       system, you may also... Read More

      These simple things, at least, you can do fairly portably.       Printing the character ’ ’ will usually give you a carriage       return without a line... Read More

      Such things depend on the terminal type (or display) you’re       using.  You will have to use a library such as termcap,       terminfo, or curses, or some... Read More

      Consult your system documentation, or ask on an appropriate       system-specific newsgroup (but check its FAQ list first).  Mouse       handling is completely... Read More

      If you can figure out how to send characters to the device at       all it’s easy enough to send escape       sequences.  In ASCII, the ESC code is 033 (27... Read More

      It’s surprisingly difficult to make this determination reliably       and portably.  Any test you make can be invalidated if the file       is created or... Read More

      The Unix and POSIX function is stat(), which several other            systems supply as well. Read More

      BSD systems provide ftruncate(), several others supply chsize(),       and a few may provide a (possibly undocumented) fcntl option       F_FREESP.  Under MS-DOS,... Read More

      There are typically at least two resource limitations on the       number of simultaneously open files: the number of low-level       "file descriptors" or "file... Read More

      Even in large memory models, MS-DOS compilers apparently toss       certain data (strings, some initialized global or static       variables) into a default data... Read More

      Set a pointer, of the appropriate type, to the right number       (using an explicit cast to assure the compiler that you really       do intend this nonportable... Read More

      Use the library function system(), which does exactly that.       Note that system’s return value is at best the command’s exit       status (although even... Read More

      argv[0] may contain all or part of the pathname, or it may       contain nothing.  You may be able to duplicate the command       language interpreter’s... Read More

      It’s hard;  Even if you can       figure out a workable way to do it, you might want to consider       making the program’s auxiliary (library)... Read More

      Unfortunately, there is no portable way.  V7 Unix, and derived       systems, provided a fairly useful ftime() function with       resolution up to a millisecond,... Read More

      The basic step is to call signal(), either as               #include <signal.h>            ... Read More

      On many systems, you can define a function matherr() which will       be called when there are certain floating-point errors, such as       errors in the math routines... Read More

      These are very particular to specific systems (PC compatibles       running MS-DOS, most likely).  You’ll get much better       information in a specific... Read More

      Those have to do with MS-DOS interrupt programming.  They don’t       exist on other systems. Read More

      You’re out of luck.  Either you misunderstood your requirement,       or it’s an impossible one to meet.  ANSI/ISO Standard C simply       does... Read More

      Either pass pointers to several locations which the function can       fill in, or have the function return a structure containing the          ... Read More

      They are pointed to by the argv array with which main() is            called. Read More

      The most portable solution is to use text files (usually ASCII),       written with fprintf() and read with fscanf() or the like.       (Similar advice also applies to... Read More

    The most straightforward thing to do is to maintain a       correspondence table of names and function pointers:               int func(),... Read More

      Use arrays of char or int, with a few macros to access the       desired bit at the proper index.  Here are some simple macros to       use with arrays of char: ... Read More

     One way is to use a pointer:               int x = 1;             if(*(char *)&x == 1)   ... Read More

      No, on both counts.  You can convert base-2 string            representations to integers with strtol(). Read More

      By picking good algorithms, implementing them carefully, and       making sure that your program isn’t doing any extra work.  For       example, the most... Read More

      Yes.         Long ago, in the early days of C, they were required, and just       enough people learned C then, and wrote code which is still in   ... Read More

      It is a macro, defined in <assert.h>, for testing "assertions".       An assertion essentially documents an assumption being made by       the programmer, an... Read More

      Some nice information and algorithms having to do with       approximate string matching, as well as a useful bibliography,       can be found in Sun Wu and Udi Manber... Read More

      C was derived from Ken Thompson’s experimental language B, which       was inspired by Martin Richards’s BCPL (Basic Combined       Programming Language),... Read More

      Simply speaking, an "lvalue" is an expression that could appear       on the left-hand sign of an assignment; you can also think of it       as denoting an object that... Read More

The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. It has since spread to many other operating systems, and is one of the most widely... Read More

Size of the final executable can be reduced using dynamic linking for libraries. Read More

There are 2 differences. First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable). Secondly,... Read More

You can’t, really. free() can , but there’s no way for your program to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release... Read More

Method is a way of doing something, especially a systematic way; implies an orderly logical arrangement (usually in steps). Read More

Even though there is no limit to the number of levels of nested include files you can have, your compiler might run out of stack space while trying to include an inordinately high number of files. This number varies according to your hardware... Read More

An internal static variable is declared inside a block with static storage class whereas an external static variable is declared outside all the blocks in a file.An internal static variable has persistent storage,block scope and no linkage.An... Read More

An array is an array of anything. A string is a specific kind of an array with a well-known convention to determine its length. There are two kinds of programming languages: those in which a string is just an array of characters, and those in... Read More

A void pointer is a C convention for a raw address. The compiler has no idea what type of object a void Pointer really points to. If you write int *ip; ip points to an int. If you write void *p; p doesn’t point to a void! In... Read More

A linker converts an object code into an executable code by linking together the necessary build in functions. The form and place of declaration where the variable is declared in a program determine the linkage of variable. Read More

Hiding the complexity. It is a process of defining communication interface for the functionality and hiding rest of the things. Read More

Adding a new method with the same name in same/derived class but with different number/types of parameters. It implements Polymorphism. Read More

It is a process in which properties of object of one class acquire the properties of object of another class. Read More

An abstract class is a special kind of class that cannot be instantiated. It normally contains one or more abstract methods or abstract properties. It provides body to a class. Read More

A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next loop iteration should occur.. Read More

Don’t get confused with the words visual and ANSI. Follow this. Visual C++ is an IDE for developing GUI(graphical user interface) real time applications using++. Visual C++ deals with more complex applicationsANSI C++ is the... Read More

A structure is a collection of pre-defined data types to create a user-defined data type. Let us say we need to create records of students. Each student has three fields: int roll_number;   char name[30];   int... Read More

Recursion: A function is called ’recursive’ if a statement within the body of a function calls the same function. It is also called ’circular definition’. Recursion is thus a process of defining something in terms of... Read More

Structures and Unions are used to store members of different data types. STRUCTURE UNION a)Declaration: struct { data type member1; data type member2; }; a)Declaration: union { data type member1; data type member2; }; ... Read More

Extern variables: belong to the External storage class and are stored in the main   memory. extern is used when we have to refer a function or variable that is   implemented in other file in the same project. The... Read More

Pass by Value: In this method, the value of each of the actual arguments in the   calling function is copied into corresponding formal arguments of the called function. In pass by value, the changes made to formal arguments in... Read More

1. Static storage class:   Storage : main memory   Default value : zero   Scope : local to the block in which the variable is defined   lifetime : till the value of the variable persists between... Read More

Out of functions fgets( ) and gets( ), fgets( ) is safer to use. gets( ) receives a string from the keyboard and it is terminated only when the enter key is hit. There is no limit for the input string. The string can be too long and may lead... Read More

realloc(): This function is used to increase or decrease the size of any dynamic   memory which is allocated using malloc() or calloc() functions. Syntax: void *realloc(void *ptr, size_t newsize);   The first... Read More

Generally when we use printf("") statement, we have to use a semicolon at the end. If printf is used inside an if condition, semicolon can be avoided. Program: Program to print some thing with out using semicolon(;) #include<stdio.h> int main... Read More

Generally when use printf("") statement we have to use semicolon at the end. If we want to print a semicolon, we use the statement: printf(";"); In above statement, we are using two semicolons. The task of printing a semicolon without using semicolon... Read More

Q : (i)What are the differences between the C statements below: char *str = "Hello"; char arr[] = "Hello"; (ii)Whether following statements get complied or not? Explain each statement. arr++; *(arr + 1) = ’s’; printf("%s",arr); ... Read More

Q : Write a program in C that returns 3 numbers from a function.       A function in C can return only one value. If we want the function to return       multiple values, we need to create a... Read More

strcpy function: copies a source string to a destination defined by user. In strcpy function both source and destination strings are passed as arguments. User should make sure that destination has enough space to accommodate the string to be copied. ... Read More

Consider a multidimensional array a[w][x][y][z]. In this array, a[i] gives address of a[i][0][0][0] and a[i]+j gives the address of a[i][j][0][0] Similarly, a[i][j] gives address of a[i][j][0][0] and a[i][j]+k gives the address of a[i][j][k][0] a[i]... Read More

Public: The data members and methods having public as access outside the class.   Protected: The data members and methods declared as protected will be accessible to the   class methods and the derived class methods only. ... Read More

  A void return type indicates that a method does not return a value. Read More

1.31b:      What’s wrong with this initialization? Read More

Q :  Why doesn’t               struct x { ... };             x thestruct;      ... Read More

      No.  There is no single, good way for a compiler to implement       implicit structure comparison (i.e. to support the == operator       for structures)... Read More

Q:   Why doesn’t the code Read More

      Not really.  Strictly speaking, C always uses pass by value.       You can simulate pass by reference yourself, by defining       functions which accept pointers... Read More

      Originally, a pointer to a function had to be "turned into" a       "real" function, with the * operator (and an extra pair of       parentheses, to keep the... Read More

      When C requires the Boolean value of an expression, a false       value is inferred when the expression compares equal to zero,       and a true value otherwise. ... Read More

      Arrays automatically allocate space, but can’t be relocated or       resized.  Pointers must be explicitly assigned to point to       allocated space ... Read More

Q:    Why doesn’t this fragment work? Read More

      It is unfortunately very easy to corrupt malloc’s internal data       structures, and the resulting problems can be stubborn.  The       most common source... Read More

      You shouldn’t have to.  A real operating system definitively       reclaims all memory and other resources when a program exits.       Nevertheless, some... Read More

      calloc(m, n) is essentially equivalent to               p = malloc(m * n);             memset(p, 0,... Read More

      Perhaps surprisingly, character constants in C are of type int,       so sizeof(’a’) is sizeof(int) (though this is another area       where C++ differs).... Read More

Yes Read More

      There is no good answer to this question.  If the values are       integers, a well-known trick using exclusive-OR could perhaps       be used, but it will not... Read More

Q:   My ANSI compiler complains about a mismatch when it sees Read More

      No.  main() must be declared as returning an int, and as       taking either zero or two arguments, of the appropriate types.       If you’re calling exit()... Read More

     The ANSI/ISO Standard says that it may do either; the behavior            is implementation-defined Read More

      Use a cast to convert the value to a known, conservatively-       sized type, then use the printf format matching that type.       For example, to print the size of a... Read More

      The functions in <locale.h> begin to provide some support for       these operations, but there is no standard routine for doing       either task.  (The... Read More

      You want an "external sort," which you can read about in Knuth,       Volume 3.  The basic idea is to sort the data in chunks (as much       as will fit in memory... Read More

      No, although poorly-written C programs do.         The tm_year field of struct tm holds the value of the year minus       1900; this field will therefore... Read More

      Make sure that you have #included <math.h>, and correctly       declared other functions returning double.  (Another library       function to be careful... Read More

      The simplest and most straightforward way is with code like               (int)(x + 0.5)         This technique won&rsquo... Read More

      Plum Hall (formerly in Cardiff, NJ; now in Hawaii) sells one;       other packages are Ronald Guilmette’s RoadTest(tm) Compiler Test       Suites (ftp to netcom... Read More

      Terminfo, some versions of termcap, and some versions of curses       have support for these non-ASCII keys.  Typically, a special key       sends a... Read More

      If the "size of a file" is the number of characters you’ll be       able to read from it in C, it is difficult or impossible to       determine this number... Read More

      Short of rewriting the file, you probably can’t.  The usual       solution is simply to rewrite the file.  (Instead of deleting       records, you... Read More

      See if you can use the opendir() and readdir() functions, which       are part of the POSIX standard and are available on most Unix       variants. ... Read More

      Unix and some other systems provide a popen() function, which       sets up a stdio stream on a pipe connected to the process       running a command, so that the... Read More

      Many "bit-fiddling" problems like this one can be sped up and       streamlined using lookup tables Read More

     The standard hoary old assembly language programmer’s trick is:               a ^= b;             b... Read More

      No.  The switch statement was originally designed to be quite       simple for the compiler to translate, therefore case labels are       limited to single,... Read More

      Hashing is the process of mapping strings to integers, usually       in a relatively small range.  A "hash function" maps a string       (or some other data... Read More

Whenever an array name appears in an expression such as - array as an operand of the sizeof operator - array as an operand of & operator - array as a string literal initializer for a character array Then the compiler does not... Read More

Pointer variable are initialized by one of the following two ways - Static memory allocation - Dynamic memory allocation Read More

No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from the main() function, you... Read More

A pointer value is a data object that refers to a memory location. Each memory location is numbered in the memory. The number attached to a memory location is called the address of the location. Read More

Normally, a function call transfers the control from the calling program to the function and after the execution of the program returns the control back to the calling program after the function call. These concepts of function saved program... Read More

A scope resolution operator (::), can be used to define the member functions of a class outside the class. Read More

It permits code reusability. Reusability saves time in program development. It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional Read More

Virtual functions are functions with the same function prototype that are defined throughout a class hierarchy. At least the base class occurrence of the function is preceded by the keyword virtual. Virtual functions are used to enable generic... Read More

A virtual function must have a definition in the class in which it is declared. A pure virtual function does not provide a definition. Classes derived directly from the abstract class must provide definitions for the inherited pure virtual... Read More

A pointer is a special variable in C language meant just to store address of any other variable or function. Pointer variables unlike ordinary variables cannot be operated with all the arithmetic operations such as ’*’,’%... Read More

1 2 3 4 5 6 7 8 9 10 Program: #include <stdio.h>   main () {   int i, j, ctr = 1;   for (i = 1; i < 5; i++) {   for (j = 1; j <= i; j++)   printf ("... Read More

Program: #include <stdio.h>   main () {   int i = 65;   int k = 120;   printf ("... Read More

1101100100111100 can be easily converted to hexadecimal numbering system. Hexa-decimal integer constants consist of combination of digits from 0 to 9 and alphabets ’A’ to ’F’. The alphabets represent numbers 10 to 15... Read More

Palindrome is a string, which when read in both forward and backward way is same. Example: radar, madam, pop, lol, rubber, etc., Program: #include<stdio.h> #include<string.h> main() { char *string1; char *string2; printf("Enter a string: ... Read More

      strncpy() was first designed to handle a now-obsolete data       structure, the fixed-length, not-necessarily--terminated       "string."  (A related quirk of... Read More

      Those functions are variously obsolete; you shouldinstead:             index?               ... Read More