C interview questions with answers

C Interview Questions Part 25

noreply@blogger.com (Anonymous) — Tue, 28 Aug 2012 06:54:00 -0700

Q:What is the difference between %d and %*d in c language?

A:%*d give the address of the variable.

eg:-
int a=10,b=20;
printf("%d%d",a,b);
printf("%*d%*d",a,b);
Result is 10 20 1775 1775
here 1775 is the starting address of the memory allocation for the integer.a and b having same address because of contagious memory allocation.

Q:What is difference between #include and #include"stdio.h" ?
A: means its a in-built header file, "stdio.h" means
its an user-defined header file

Q:What is the difference between i++ and i+1 ?

A:i++ is an increment and assign to i but i+1 is just an increment of i, but it doesnt mean the value in i got changed here.

Q:Difference between for loop and while loop?

A:In for loop we should know initial &last condition.....but in while loop we only know the last condition....
ex. of for loop..for(i=0;i<=10;i++){
printf("%d",i);
}
ex. of while loop..while(i<=10){
printf("%d",i);
i++;
}

Q:Difference between structure and union?
A:Union allocates the memory equal to the maximum memory required by the member of the union but structure allocates the memory equal to the total memory required by the members.

Q:Difference between *p and **p?
A:*p is a simple pointer which holds the address of another variable while **p is a double pointer which holds address of the pointer in which actual address of the another variable is stored.

Q:What is the difference between macros and inline functions?
A:Macro- does not involve in compilation if there is any logical error also just replaces the code inline- look like function, but control doesn't goes to function and execute, it simply replaces the code like macro but involves in compilation.

C Interview Questions Part 24

noreply@blogger.com (Anonymous) — Mon, 6 Aug 2012 10:27:00 -0700

Q:What is void pointer?
A:Void pointer is the pointer which itself is null and can not be interchanged by others.
Ex-
{
int *a;
void *b;
*a=*b; //valid
a=b; //invalid
}

Q:What are the advantages of pointers?

A:Pointer variable is used to store the memory address of the another variable.Using pointers we can directly manipulate or access memory which is faster hence it increases execution time.

Q:What is the difference between structure and union?
A:union is unified memory where structure is non unified memory.All members of structure occupy consecutive chunks of memory and union members will share the most highest memory of the union member.i.e data type.we can access all the members of structure at a time but in union we can access a single union member at a time.

Q:Write a c program for greatest of three numbers without using if statement main( )?
A:{
int a,b,c,s1,big;
printf("enter 3 values");
scanf("%d %d %d", &a,&b,&c);
s1=(a>b)? a : b;
big= (s1>c)? s1 : c;
printf("largest of 3 no's=%d",big);
}

Q:What is the difference between definition and declaration? give me some example declaration?

A:for example,int i;
definition:
declaration as well as initialisation is known as definition
for example int i=25;

Q:What is the exact difference between '\0' and "" ?

A:'\0' is NULL character and "" is null string.

Q:Write a program to print infinite number?

A:void main(){
int i;
clrscr ();
for(i=0;;i++)
{
printf ("%d",&i);
}
getch ();
}

C Interview Questions Part 23

noreply@blogger.com (Anonymous) — Sun, 29 Jul 2012 09:43:00 -0700

Q:Why C Language is platform dependent?
A:c is a Structure oriented programming language and it doesn't generate any byte code which can't be run on any operating system with this disadvantage C don't become a platform independent.

Q:How will you allocate memory to double a pointer?
A:main()
{
char *pch; **ppch;
pch = malloc(100);
if(pch == NULL)
return -1;
ppch = &pch;
}

Q:Difference between ordinary variable and pointer in C?
A:An ordinary variable is like a container it can hold any value and we can change the value of ordinary variable at time throughout the program. A pointer is a variable that stores the address of another variable

Q:How to swap two integers 1 and 32767 without using third variable?
A:Below logic can be used to swap for the required condition:
a=1;
b=32767;
a=a+b;
b=a-b;
a=a-b;

Q:Which operator is known as dummy operator in c?
A:unary + is the only dummy operator in c

Q:What is pre-processor?
A:Preprocessor directives are not the libraries which should be included while writing a program .But it is a notation used to include the libraries which are included in the header part of a program

Q:What is void pointer?
A:Void pointer is the pointer which itself is null and can not be interchanged by others.
Example:
{
int *a;
void *b;

*a=*b; //valid
a=b; //invalid
}

C Interview Questions Part 22

noreply@blogger.com (Anonymous) — Sun, 24 Jun 2012 11:01:00 -0700

Q:Why n++ executes quicker compared to n+1 ?
A:The expression n++ needs a single machine instruction such as INR to carry out the increment operation whereas, n+1 needs more instructions to carry out this operation.

Q:What is the purpose of main( ) function ?
A:The function main( ) invokes other functions within it.It is the first function to be called when the program starts execution.It returns an int value to the environment that called the program.Recursive call is allowed for main( ) also.It has two arguments 1)argument count and 2) argument vector (represents strings passed).

Q:What is the simplest sorting method to use?
A:The answer is the standard library function qsort(). It is already written and already debugged and also it has been optimized as much as possible (usually).

Void qsort(void *buf, size_t num, size_t size, int (*comp)(const void *ele1, const void *ele2));

Q:What will the preprocessor do for a program?
A:The C preprocessor is used to modify your program according to the preprocessor directives in your source code. A preprocessor directive is a statement (such as #define) that provides the preprocessor specific instructions on how to modify your source code.

The preprocessor is actually invoked as the 1st part of your compiler program’s compilation step. It is usually hidden from the programmer since it is run automatically by the compiler.The preprocessor reads in all of your include files and the source code you are compiling and creates a preprocessed version of your source code. This preprocessed version has all of its macros and constant symbols replaced by their corresponding code and value assignments.If your source code consists of any conditional preprocessor directives (such as #if), the preprocessor evaluates the condition and modifies your source code accordingly.

Q:Is it better to use a macro or a function ?
A:The answer depends upon the situation you are writing code for. Macros have the distinct advantage of being more efficient (and faster) than functions, because their corresponding code is actually inserted directly into your source code at the point where the macro is called.However, macros are often small and cannot handle large, complex coding constructs.Thus, the choice between using a macro and using a function is one of deciding between the tradeoff of faster program speed versus smaller program size. Generally, you should use macros to replace small, repeatable code sections, and you should utilize functions for larger coding tasks that may need several lines of code.

C Interview Questions Part 21

noreply@blogger.com (Anonymous) — Wed, 6 Jun 2012 11:43:00 -0700

Q:Way to minimize a last dimension regarding executable?
A:Dimension in the remaining executable is usually minimized employing strong relating with regard to
your local library

Q:Variation among const char* p in addition to char const* p?
A:Within const char* p, that nature directed through ‘p’ is actually frequent, therefore we cant alter the worthiness regarding nature directed through p nonetheless oughout could make ‘p’ make reference to another spot.Within char const* p, that ptr ‘p’ is actually frequent not necessarily that nature referenced through the idea, therefore oughout cant help make ‘p’ to be able to benchmark to be able to any spot nonetheless we may alter the worthiness in the char directed through ‘p’.

Q:How will you decide the type of your allotted piece regarding storage area?
A:A person can’t, truly. free()#) may, nonetheless there’s not a way on your system to be able to learn that magic free()#) employs. Even though you disassemble that collection in addition to reduced magic, there’s absolutely no assure that magic won’t alter with all the up coming relieve in the compiler.

Q:How much does static varied signify?
A:There are actually three major employs for any static.
one particular in case you state with a perform:The idea stores the worthiness among perform message or calls a couple of. When it really is reported for any perform title:Through default perform is actually extern.. therefore most effective for you accessible through additional records in the event the perform report is actually since static.. it really is invisible for any external records several. Static with regard to world issues:Through default you can utilize the world issues through outdoor records When it really is static world.. which varied is actually constrained to be able to by using from the report.

Q:Can you tell me how to check whether a linked list is circular?
A: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 ("circular");
}}

C Interview Questions Part 20

noreply@blogger.com (Anonymous) — Sun, 3 Jun 2012 09:41:00 -0700

Q:Can include records end up being nested?
A:Certainly. Incorporate records might be nested any number regarding situations. So long as you use precautionary actions, you can stay away from including the same report two times. In the past, nesting header records appeared to be noticed since awful licensed users training, because doing so complicates that dependency administering perform in the help make system and therefore slows along collection. Nearly all today’s famous compilers constitute because of this frustration through putting into action any idea referred to as pre compiled headers, through which almost all headers in addition to linked dependencies tend to be saved in the pre compiled state.

A good number of developers love to create a custom made header report which includes #include phrases for each header necessary for every module. This can be completely satisfactory and may aid stay away from potential wounds with regards to #include records, for example by chance omitting a good #include report in the module.

Q:What is a null pointer?
A: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* or char*.

Some people, notably C++ programmers, prefer to use 0 rather than NULL.
The null pointer is used in three ways:
1) To stop indirection in a recursive data structure.
2) As an error value.
3) As a sentinel value.

Q:What is the difference between printf() and sprintf()?
A:sprintf() writes data to the character array whereas printf(...) writes data to the standard output device.

Q:What is the output of printf("%d") ?
A: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 in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on the format specification string. Now when we write printf("%d",a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location.

3. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(...) and scanf(...).
malloc()

C Interview Questions Part 19

noreply@blogger.com (Anonymous) — Thu, 3 May 2012 11:05:00 -0700

Q:Exactly what does static variable indicate?
A:There are actually three major purposes of the static.
1. If you declare inside a function:
It keeps the value between function calls
2.If it is declared for a function name:
By default function is actually extern.therefore it is going to be visible from all other files if the function declaration is as static..it is invisible for the external files
3. Static for global variables:
By default we are able to make use of the global variables from outside files when it is static global..that variable is restricted to with in the file.

Q:What are the various storage classes within C?
A:C has 3 kinds of storage: automatic, static and allocated.
Variable getting block scope and also without having static specifier have automatic storage duration.
Variables along with block scope, and with static specifier have static scope. Global variables (i.e, file scope) with or without the static specifier also provide static scope.
Memory extracted from calls to malloc(), alloc() or realloc() is allocated storage class.

Q:Can static variables be declared within a header file?
A:you can not declare a static variable without defining it as well (this is really because the actual storage class modifiers static and also extern are mutually exclusive). A static variable could be defined in a header file, but this would cause each source file that included the header file to get its very own private copy from the variable, which is most likely not what was meant

Q:Can a variable become both constant and volatile?
A:Yes. The const modifier implies that this particular program code cannot change the value of the actual variable, but that will not imply that the value can not be changed by means outside this code. For instance, within the example in frequently asked questions, the timer structure was accessed through a volatile const pointer.The function by itself did not change the value of the timer, so it had been declared const. However, the value had been changed by hardware on the computer, so it was declared volatile. If a variable is both equally const and volatile, the two modifiers can come in either order.

C Interview Questions Part 18

noreply@blogger.com (Anonymous) — Tue, 24 Jan 2012 10:10:00 -0800

Q:What is the difference between ordinary variable and pointer in C?
A: An ordinary variable is like a container it can hold any value and we can change the value of ordinary variable at a time throughout the program .A pointer is a variable that stores the address of another Variable.

Q:What are segment and offset addresses?
A: When paging technique is performed, the page will breaks into segments and its sequence is said to be segments and its width can be said as offset. In short,segment is a physical address and offset is logical address.

Q:What is "far" and "near" pointers in "c" ?
A:“Near" and "far" pointers are actually non-standard qualifiers that you'll find only on x86 systems. They reflect the odd segmentation architecture of Intel processors. In short, a near pointer is an offset only,which refers to an address in a known segment. A far pointer is a compound value, containing both a segment number and an offset into that segment. Segmentation still exists on Intel processors, but it is not used in any of the mainstream 32-bit operating systems developed for them, so you'll generally only find the "near" and "far" keywords in source code developed for Windows 3.x,MS-DOS, Xenix/80286, etc.

Q:When should a type cast be used?
A:There are two situations in which to use a type cast. The first use is to change the type of an operand to an arithmetic operation so that the operation will be performed properly.
The second case is to cast pointer types to and from void * in order to interface with functions that expect or return void pointers. For example, the following line type casts the return value of the call to malloc() to be a pointer to a foo structure.
struct foo *p = (struct foo *) malloc(sizeof(struct foo));

Q:What is the difference between %d and %*d in c language?
A: %d give the original value of the variable and %*d give the address of the variable.
eg:-int a=10,b=20;
printf("%d%d",a,b);
printf("%*d%*d",a,b);
Result is 10 20 1775 1775 .Here 1775 is the starting address of the memory allocation for the integer.a and b having same address because of contagious memory allocation.

C Interview Questions Part 17

noreply@blogger.com (Anonymous) — Fri, 26 Aug 2011 11:15:00 -0700

Q:What is the difference between "calloc(...)" and "malloc(...)"?
A: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 which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...).
2. malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available calloc(...) allocates an array in memory with elements initialized to and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C++ _set_new_mode function to set the new handler mode.

Q:What is the difference between "printf(...)" and"sprintf(...)"?

A:sprintf(...) writes data to the character array whereas printf(...) writes data to the
standard output device.

Q:What does static variable mean?
A: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 function declaration is as static..it is invisible for the outer files
3. Static for global variables:By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file

Q:What are the differences between malloc() and calloc()?
A: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, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

Q:Difference between const char* p and char const* p?
A: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 the character referenced by it, so u cant make ‘p’ to reference to any other location but u can change the value of the char pointed by ‘p’.

Q:How can you determine the size of an allocated portion of memory?
A: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 of the compiler.

C Interview Questions Part 16

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:53:00 -0800

Q: What is C language?
A: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 used programming languages. C is prized for its efficiency, and is the most popular programming language for writing system software, though it is also used for writing applications.

Q: Inprintf() Function What is the output of printf("%d")?
A:1. When we write printf("%d",x); this means compiler will print the value of x. But as here, there is nothing after ï¿½%dï¿½ so compiler will show in output window garbage value.

2. When we use %d the compiler internally uses it to access the argument in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on the format specification string. Now when we write printf("%d",a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location.

3. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(...) and
scanf(...).

Q:Why doesn't the following code give the desired result?
int x = 3000, y = 2000 ;
long int z = x * y ;
A: Here the multiplication is carried out between two ints x and y, and the result that would overflow would be truncated before being assigned to the variable z of type long int. However, to get the correct output, we should use an explicit cast to force long arithmetic as shown below:

long int z = ( long int ) x * y ;
Note that ( long int )( x * y ) would not give the desired effect.

Q: Why doesn't the following statement work?char str[ ] = "Hello" ;
strcat ( str, '!' ) ;
A: The string function strcat( ) concatenates strings and not a character. The basic difference between a string and a character is that a string is a collection of characters, represented by an array of characters whereas a character is a single character. To make the above statement work writes the statement as shown below:
strcat ( str, "!" ) ;

Q:Malloc() Function- What is the difference between "calloc(...)" and "malloc(...)"?

A: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 which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...).

2.malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available.
calloc(...) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C++ _set_new_mode function to set the new handler mode.

C Interview Questions Part 15

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:45:00 -0800

Q:How do I write code to get the current drive as well as set the current drive?

A: The function getdisk( ) returns the drive number of current drive. The drive number 0 indicates 'A' as the current drive, 1 as 'B' and so on. The Setdisk( ) function sets the current drive. This function takes one argument which is an integer indicating the drive to be set. Following program demonstrates use of both the functions.

#include

main( )

{

int dno, maxdr ;

dno = getdisk( ) ;

printf ( "\nThe current drive is: %c\n", 65 + dno

) ;

maxdr = setdisk ( 3 ) ;

dno = getdisk( ) ;

printf ( "\nNow the current drive is: %c\n", 65 +

dno ) ;

}

Q: How do I compare character data stored at two different memory locations?

A: Sometimes in a program we require to compare memory ranges containing strings. In such a situation we can use functions like memcmp( ) or memicmp( ). The basic difference between two functions is that memcmp( ) does a case-sensitive comparison whereas memicmp( ) ignores case of characters. Following program illustrates the use of both the functions.

#include

main( )

{

char *arr1 = "Kicit" ;

char *arr2 = "kicitNagpur" ;

int c ;

c = memcmp ( arr1, arr2, sizeof ( arr1 ) ) ;

if ( c == 0 )

printf ( "\nStrings arr1 and arr2 compared using memcmp are identical" ) ;

else

printf ( "\nStrings arr1 and arr2 compared using memcmp are not identical") ;

c = memicmp ( arr1, arr2, sizeof ( arr1 ) ) ;

if ( c == 0 )

printf ( "\nStrings arr1 and arr2 compared using memicmp are identical" );

else

printf ( "\nStrings arr1 and arr2 compared using memicmp are not identical" ) ;

}

Fixed-size objects are more appropriate as compared to variable size data objects. Using variable-size data objects saves very little space. Variable size data objects usually have some overhead. Manipulation of fixed-size data objects is usually faster and easier. Use fixed size when maximum size is clearly bounded and close to average. And use variable-size data objects when a few of the data items are bigger than the average size. For example,

char *num[10] = { "One", "Two", "Three", "Four",

"Five", "Six", "Seven", "Eight", "Nine", "Ten" } ;

Instead of using the above, use

char num[10][6] = { "One", "Two", "Three", "Four",

"Five", "Six", "Seven", "Eight", "Nine", "Ten" } ;

The first form uses variable-size data objects. It allocates 10 pointers, which are pointing to 10 string constants of variable size. Assuming each pointer is of 4 bytes, it requires 90 bytes. On the other hand, the second form uses fixed size data objects. It allocates 10 arrays of 6 characters each. It requires only 60 bytes of space. So, the variable-size in this case does not offer any advantage over fixed size.

C Interview Questions Part 14

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:42:00 -0800

Q:When we open a file, how does functions like fread( )/fwrite( ), etc. get to know from where to read or to write the data?

A: When we open a file for read/write operation using function like fopen( ), it returns a pointer to the structure of type FILE. This structure stores the file pointer called position pointer, which keeps track of current location within the file. On opening file for read/write operation, the file pointer is set to the start of the file. Each time we read/write a character, the position pointer advances one character. If we read one line of text at a step from the file, then file pointer advances to the start of the next line. If the file is opened in append mode, the file pointer is placed at the very end of the file. Using fseek( ) function we can set the file pointer to some other place within the file

Q: Explain the use of array indices ?

A:If we wish to store a character in a char variable ch and the character to be stored depends on the value of another variable say color (of type int), then the code would be as shown below:

switch ( color )

{

case 0 :

ch = 'R' ;

break ;

case 1 :

ch = 'G' ;

break ;

case 2 :

ch = 'B' ;

break ;

}

In place of switch-case we can make use of the value in color as an index for a character array. How to do this is shown in following code snippet.

char *str = "RGB' ;

char ch ;

int color ;

// code

ch = str[ color ] ;

Q:How do I write code that would get error number and display error message if any standard error occurs?

A: Following code demonstrates this.

#include

main( )

{

char *errmsg ;

FILE *fp ;

fp = fopen ( "C:\file.txt", "r" ) ;

if ( fp == NULL )

{

errmsg = strerror ( errno ) ;

printf ( "\n%s", errmsg ) ;

}

Here, we are trying to open 'file.txt' file. However, if the file does not exist, then it would cause an error. As a result, a value (in this case 2) related to the error generated would get set in errno. errno is an external int variable declared in 'stdlib.h' and also in 'errno.h'. Next, we have called sterror( ) function which takes an error number and returns a pointer to standard error message related to the given error number.

C Interview Questions Part 13

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:40:00 -0800

Q:How do I determine amount of memory currently available for allocating?

A: We can use function coreleft( ) to get the amount of memory available for allocation. However, this function does not give an exact amount of unused memory. If, we are using a small memory model, coreleft( ) returns the amount of unused memory between the top of the heap and stack. If we are using a larger model, this function returns the amount of memory between the highest allocated memory and the end of conventional memory. The function returns amount of memory in terms of bytes.

Q:How does a C program come to know about command line arguments?

A: When we execute our C program, operating system loads the program into memory. In case of DOS, it first loads 256 bytes into memory, called program segment prefix. This contains file tables,environment segment, and command line information. When we compile the C program the compiler inserts additional code that parses the command, assigning it to the argv array, making the arguments easily accessible within our C program.

Q:What is environment and how do I get environment for a specific entry?

A: While working in DOS, it stores information in a memory region called environment. In this region we can place configuration settings such as command path, system prompt, etc. Sometimes in a program we need to access the information contained in environment. The function getenv( ) can be used when we want to access environment for a specific entry. Following program demonstrates the use of this function.

#include

main( )

{

char *path = NULL ;

path = getenv ( "PATH" ) ;

if ( *path != NULL )

printf ( "\nPath: %s", path ) ;

else

printf ( "\nPath is not set" ) ;

}

Q:How do I display current date in the format given below?

Saturday October 12, 2002

A: Following program illustrates how we can display date in above given format.

#include

main( )

{

struct tm *curtime ;

time_t dtime ;

char str[30] ;

time ( &dtime ) ;

curtime = localtime ( &dtime ) ;

strftime ( str, 30, "%A %B %d, %Y", curtime ) ;

printf ( "\n%s", str ) ;

}

Here we have called time( ) function which returns current time. This time is returned in terms of seconds, elapsed since 00:00:00 GMT, January 1, 1970. To extract the week day, day of month, etc.from this value we need to break down the value to a tm structure. This is done by the function localtime( ). Then we have called strftime( ) function to format the time and store it in a string str.

C Interview Questions Part 12

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:33:00 -0800

Q:Can we get the mantissa and exponent form of a given number?

A:The function frexp( ) splits the given number into a mantissa and exponent form. The function takes two arguments, the number to be converted as a double value and an int to store the exponent form. The function returns the mantissa part as a double value. Following example demonstrates the use of this function.

#include
void main( )
{

double mantissa, number ;

int exponent ;

number = 8.0 ;

mantissa = frexp ( number, &exponent ) ;

printf ( "The number %lf is ", number ) ;

printf ( "%lf times two to the ", mantissa ) ;

printf ( "power of %d\n", exponent ) ;

return 0 ;

}

Q:What is access( ) function...

A:The access( ) function checks for the existence of a file and also determines whether it can be read,written to or executed. This function takes two arguments the filename and an integer indicating the access mode. The values 6, 4, 2, and 1 checks for read/write, read, write and execute permission of a given file, whereas value 0 checks whether the file exists or not. Following program demonstrates how we can use access( ) function to check if a given file exists.

#include

main( )

{

char fname[67] ;

printf ( "\nEnter name of file to open" ) ;

gets ( fname ) ;

if ( access ( fname, 0 ) != 0 )

{

printf ( "\nFile does not exist." ) ;

return ;

}

Q:How do I convert a floating-point number to a string?

A: Use function gcvt( ) to convert a floating-point number to a string. Following program demonstrates the use of this function.

#include

main( )

{

char str[25] ;

float no ;

int dg = 5 ; /* significant digits */

no = 14.3216 ;

gcvt ( no, dg, str ) ;

printf ( "String: %s\n", str ) ;

}

C Interview Questions Part 11

noreply@blogger.com (Anonymous) — Sun, 5 Dec 2010 10:31:00 -0800

Q:How can I find the day of the week of a given date?

A: The following code snippet shows how to get the day of week from the given date.

dayofweek ( int yy, int mm, int dd )

{

/*Monday = 1 and Sunday = 0 */

/* month number >= 1 and <= 12, yy > 1752 or so */

static int arr[ ] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 } ;

yy = yy - mm < 3 ;

return ( yy + yy / 4 - yy / 100 + yy / 400 + arr[ mm - 1] + dd ) % 7 ;

}

void main( )

{

printf ( "\n\n\nDay of week : %d ", dayofweek ( 2002, 5, 18 ) ) ;

}

Q:What's the difference between these two declarations?

struct str1 { ... } ;

typedef struct { ... } str2 ;

A: The first form declares a structure tag whereas the second declares a typedef. The main difference is that the second declaration is of a slightly more abstract type -- its users don't necessarily know that it is a structure, and the keyword struct is not used when declaring instances of it.

Q: How do I print the contents of environment variables?

A: The following program shows how to achieve this:

main( int argc, char *argv[ ], char *env[ ] )

{

int i = 0 ;

clrscr( ) ;

while ( env[ i ] )

printf ( "\n%s", env[ i++ ] ) ;

}

main( ) has the third command line argument env, which is an array of pointers to the strings. Each pointer points to an environment variable from the list of environment variables.

Q:How do I use the function ldexp( ) in a program?

A: The math function ldexp( ) is used while solving the complex mathematical equations. This function takes two arguments, a double value and an int respectively. The order in which ldexp( ) function performs calculations is ( n * pow ( 2, exp ) ) where n is the double value and exp is the integer. The following program demonstrates the use of this function.

#include

void main( )

{

double ans ;

double n = 4 ;

ans = ldexp ( n, 2 ) ;

printf ( "\nThe ldexp value is : %lf\n", ans ) ;

}

Here, ldexp( ) function would get expanded as ( 4 * 2 * 2 ), and the output would be the ldexp value is : 16.000000

C Interview Questions Part 10

noreply@blogger.com (Anonymous) — Tue, 2 Feb 2010 12:09:00 -0800

Q:How do I write code that executes certain function only at program termination?

A: Use atexit( ) function as shown in following program.

#include

main( )

{

int ch ;

void fun ( void ) ;

atexit ( fun ) ;

// code

}

void fun( void )

{

printf ( "\nTerminate program......" ) ;

getch( ) ;

}

Q:What are memory models?

A: The compiler uses a memory model to determine how much memory is allocated to the program. The PC divides memory into blocks called segments of size 64 KB. Usually, program uses one segment for code and a second segment for data. A memory model defines the number of segments the compiler can use for each. It is important to know which memory model can be used for a program. If we use wrong memory model, the program might not have enough memory to execute. The problem can be solved using larger memory model. However, larger the memory model, slower is your program execution. So we must choose the smallest memory model that satisfies our program needs. Most of the compilers support memory models like tiny, small, medium, compact, large and huge.

Q:How does C compiler store elements in a multi-dimensional array?

A:The compiler maps multi-dimensional arrays in two ways—Row major order and Column order. When the compiler places elements in columns of an array first then it is called column-major order. When the compiler places elements in rows of an array first then it is called row-major order. C compilers store multidimensional arrays in row-major order. For example, if there is a multi-dimensional array a[2][3], then according row-major order, the elements would get stored in memory following order:

a[0][0], a[0][1], a[0][2], a[1][0], a[1][1], a[1][2]

Q:If the result of an _expression has to be stored to one of two variables, depending on a condition, can we use conditional operators as shown below?

( ( i < 10 ) ? j : k ) = l * 2 + p ;

A: No! The above statement is invalid. We cannot use the conditional operators in this fashion. The conditional operators like most operators, yields a value, and we cannot assign the value of an _expression to a value. However, we can use conditional operators as shown in following code snippet.

main( )

{

int i, j, k, l ;

i = 5 ; j = 10 ; k = 12, l = 1 ;

* ( ( i < 10 ) ? &j : &k ) = l * 2 + 14 ;

printf ( "i = %d j = %d k = %d l = %d", i, j, k, l ) ;

}

The output of the above program would be as given below:

i = 5 j = 16 k = 12 l = 1

C Interview Questions Part 9

noreply@blogger.com (Anonymous) — Fri, 5 Jun 2009 12:07:00 -0700

Q: What is a stack ?

A: The stack is a region of memory within which our programs temporarily store data as they execute. For example, when a program passes parameters to functions, C places the parameters on the stack. When the function completes, C removes the items from the stack. Similarly, when a function declares local variables, C stores the variable's values on the stack during the function's execution. Depending on the program's use of functions and parameters, the amount of stack space that a program requires will differ.

Q:Allocating memory for a 3-D array

A: #include "alloc.h"

#define MAXX 3

#define MAXY 4

#define MAXZ 5

main( )

{

int ***p, i, j, k ;

p = ( int *** ) malloc ( MAXX * sizeof ( int ** ) ) ;

for ( i = 0 ; i < MAXX ; i++ )

{

p[i] = ( int ** ) malloc ( MAXY * sizeof ( int * ) ) ;

for ( j = 0 ; j < MAXY ; j++ )

p[i][j] = ( int * ) malloc ( MAXZ * sizeof ( int ) ) ;

}

for ( k = 0 ; k < MAXZ ; k++ )

{

for ( i = 0 ; i < MAXX ; i++ )

{

for ( j = 0 ; j < MAXY ; j++ )

{

p[i][j][k] = i + j + k ;

printf ( "%d ", p[i][j][k] ) ;

}

printf ( "\n" ) ;

}

printf ( "\n\n" ) ;

}

Q:How to distinguish between a binary tree and a tree?

A: A node in a tree can have any number of branches. While a binary tree is a tree structure in which any node can have at most two branches. For binary trees we distinguish between the subtree on the left and subtree on the right, whereas for trees the order of the subtrees is irrelevant.

Consider two binary trees, but these binary trees are different. The first has an empty right subtree while the second has an empty left subtree. If the above are regarded as trees (not the binary trees), then they are same despite the fact that they are drawn differently. Also, an empty binary tree can exist, but there is no tree having zero nodes.

C Interview Questions Part 8

noreply@blogger.com (Anonymous) — Wed, 27 May 2009 12:05:00 -0700

Q:If we have declared an array as global in one file and we are using it in another file then why doesn't the sizeof operator works on an extern array?

A: An extern array is of incomplete type as it does not contain the size. Hence we cannot use sizeof operator, as it cannot get the size of the array declared in another file. To resolve this use any of one the following two solutions:

1. In the same file declare one more variable that holds the size of array. For example,

array.c

int arr[5] ;

int arrsz = sizeof ( arr ) ;

myprog.c

extern int arr[] ;

extern int arrsz ;

2. Define a macro which can be used in an array

declaration. For example,

myheader.h

#define SZ 5

array.c

#include "myheader.h"

int arr[SZ] ;

myprog.c

#include "myheader.h"

extern int arr[SZ] ;

Q:How do I write printf( ) so that the width of a field can be specified at runtime?

A: This is shown in following code snippet.

main( )

{

int w, no ;

printf ( "Enter number and the width for the

number field:" ) ;

scanf ( "%d%d", &no, &w ) ;

printf ( "%*d", w, no ) ;

}

Here, an '*' in the format specifier in printf( ) indicates that an int value from the argument list should be used for the field width.

Q:How to find the row and column dimension of a given 2-D array?

A: Whenever we initialize a 2-D array at the same place where it has been declared, it is not necessary to mention the row dimension of an array. The row and column dimensions of such an array can be determined programmatically as shown in following program.

void main( )

{

int a[][3] = { 0, 1, 2,9,-6, 8,7, 5, 44,23, 11,15 } ;

int c = sizeof ( a[0] ) / sizeof ( int ) ;

int r = ( sizeof ( a ) / sizeof ( int ) ) / c ;

int i, j ;

printf ( "\nRow: %d\nCol: %d\n", r, c ) ;

for ( i = 0 ; i < r ; i++ )

{

for ( j = 0 ; j < c ; j++ )

printf ( "%d ", a[i][j] ) ;

printf ( "\n" ) ;

}

C Interview Questions Part 7

noreply@blogger.com (Anonymous) — Thu, 14 May 2009 11:57:00 -0700

Q:What is atexit() ?

A:Function atexit( ) recevies parameter as the address of function of the type void fun ( void ). The function whose address is passed to atexit( ) gets called before the termination of program. If atexit( ) is called for more than one function then the functions are called in "first in last out" order. You can verify that from the output.

#include

void fun1( )

{

printf("Inside fun1\n");

}

void fun2( )

{

printf("Inside fun2\n");

}

main( )

{

atexit ( fun1 ) ;

/* some code */

atexit ( fun2 ) ;

printf ( "This is the last statement of

program?\n" );

}

Q:How do I write a user-defined function, which deletes each character in a string str1, which matches any character in string str2?

A: The function is as shown below:

Compress ( char str1[], char str2[] )

{

int i, j, k ;

for ( i = k = 0 ; str1[i] != ‘\0’ ; i++ )

{

for ( j = 0 ; str2[j] != ‘\0’ && str2[j] !=

str1[i] ; j++ );

if ( str2[j] == ‘\0’ )

str1[k++] = str1[I] ;

}

str1[k] = ‘\0’

}

Q:How does free( ) know how many bytes to free?

A: The malloc( ) / free( ) implementation remembers the size of each block allocated and returned, so it is not necessary to remind it of the size when freeing.

Q:What is the use of randomize( ) and srand( ) function?

A: While generating random numbers in a program, sometimes we require to control the series of numbers that random number generator creates. The process of assigning the random number generators starting number is called seeding the generator. The randomize( ) and srand( ) functions are used to seed the random number generators. The randomize( ) function uses PC's clock to produce a random seed, whereas the srand( ) function allows us to specify the random number generator's starting value.

C Interview Questions Part 6

noreply@blogger.com (Anonymous) — Tue, 21 Apr 2009 11:48:00 -0700

Q:The sizeof( ) function doesn’t return the size of the block of memory pointed to by a pointer. Why?

A:The sizeof( ) operator does not know that malloc( ) has been used to allocate a pointer. sizeof( ) gives us the size of pointer itself. There is no handy way to find out the size of a block allocated by malloc( ).

Q: What is FP_SEG And FP_OFF…

A:Sometimes while working with far pointers we need to break a far address into its segment and offset. In such situations we can use FP_SEG and FP_OFF macros. Following program illustrates the use of these two macros.

#include

main( )

{

unsigned s, o ;

char far *ptr = "Hello!" ;

s = FP_SEG ( ptr ) ;

o = FP_OFF ( ptr ) ;

printf ( "\n%u %u", s, o ) ;

}

Q:How do I write a program to convert a string containing number in a hexadecimal form to its equivalent decimal?

A: The following program demonstrates this:

main( )

{

char str[] = "0AB" ;

int h, hex, i, n ;

n = 0 ; h = 1 ;

for ( i = 0 ; h == 1 ; i++ )

{

if ( str[i] >= '0' && str[i] <= '9' )

hex = str[i] - '0' ;

else

{

if ( str[i] >= 'a' && str[i] <= 'f' )

hex = str[i] - 'a' + 10 ;

else

if ( str[i] >= 'A' && str[i] <= 'F' )

hex = str[i] - 'A' + 10 ;

else

h = 0 ;

}

if ( h == 1 )

n = 16 * n + hex ;

}

printf ( "\nThe decimal equivalent of %s is %d",

str, n ) ;

}

The output of this program would be the decimal equivalent of 0AB is 171.

Q:How do I write code that reads the segment register settings?

A: We can use segread( ) function to read segment register settings. There are four segment registers—code segment, data segment, stack segment and extra segment. Sometimes when we use DOS and BIOS services in a program we need to know the segment register's value. In such a situation we can use segread( ) function. The following program illustrates the use of this function.

#include

main( )

{

struct SREGS s ;

segread ( &s ) ;

printf ( "\nCS: %X DS: %X SS: %X ES: %X",s.cs,

s.ds, s.ss, s.es ) ;

}

C Interview Questions Part 5

noreply@blogger.com (Anonymous) — Tue, 14 Apr 2009 11:46:00 -0700

Q:Explain the functions memcmp( ) and memicmp( )

A:The functions memcmp( ) and memicmp( ) compares first n bytes of given two blocks of memory or strings.However, memcmp( ) performs comparison as unsigned chars whereas memicmp( ) performs comparison as chars but ignores case (i.e. upper or lower case). Both the functions return an integer value where 0 indicates that two memory buffers compared are identical. If the value returned is greater than 0 then it indicates that the first buffer is bigger than the second one. The value less than 0 indicate that the first buffer is less than the second buffer. The following code snippet demonstrates use of both

#include

main( )

{

char str1[] = "This string contains some

characters" ;

char str2[] = "this string contains" ;

int result ;

result = memcmp ( str1, str2, strlen ( str2 ) ) ;

printf ( "\nResult after comapring buffer using

memcmp( )" ) ;

show ( result ) ;

result = memicmp ( str1, str2, strlen ( str2 ) ) ;

printf ( "\nResult after comapring buffer using

memicmp( )" ) ;

show ( result ) ;

}

show ( int r )

{

if ( r == 0 )

printf ( "\nThe buffer str1 and str2 hold

identical data" ) ;

if ( r > 0 )

printf ( "\nThe buffer str1 is bigger than buffer

str2" ) ;

if ( r < 0 )

printf ( "\nThe buffer str1 is less than buffer

str2" ) ;

Q:How do I write code to find an amount of free disk space available on current drive?

A: Use getdfree( ) function as shown in follow code.

#include

main( )

{

int dr ; struct dfree disk ;

long freesp ;

dr = getdisk( ) ;

getdfree ( dr + 1 , &disk ) ;

if ( disk.df_sclus == 0xFFFF )

{

printf ( "\ngetdfree( ) function failed\n");

exit ( 1 ) ;

}

freesp = ( long ) disk.df_avail

* ( long ) disk.df_bsec

* ( long ) disk.df_sclus ;

printf ( "\nThe current drive %c: has %ld bytes

available as free space\n", 'A' + dr, freesp ) ;

}

C Interview Questions Part 4

noreply@blogger.com (Anonymous) — Fri, 27 Mar 2009 11:42:00 -0700

Q:Are the following two statements identical?
char str[6] = "Kicit" ;
char *str = "Kicit" ;
A: No! Arrays are not pointers. An array is a single, pre-allocated chunk of contiguous elements (all of the same type), fixed in size and location. A pointer on the other hand, is a reference to any data element (of a particular type) located anywhere. A pointer must be assigned to point to space allocated elsewhere, but it can be reassigned any time. The array declaration char str[6] ; requests that space for 6 characters be set aside, to be known by name str. In other words there is a location named str at which six characters are stored. The pointer declaration char *str ; on the other hand, requests a place that holds a pointer, to be known by the name str. This pointer can point almost anywhere to any char, to any contiguous array of chars, or nowhere.

Q:Is the following code fragment correct?

const int x = 10 ;

int arr[x] ;

A: No! Here, the variable x is first declared as an int so memory is reserved for it. Then it is qualified by a const qualifier. Hence, const qualified object is not a constant fully. It is an object with read only attribute, and in C, an object associated with memory cannot be used in array dimensions.

Q:How do I write code to retrieve current date and time from the system and display it as a string?

A:Use time( ) function to get current date and time and then ctime( ) function to display it as a string. This is shown in following code snippet.

#include

void main( )

{

time_t curtime ;

char ctm[50] ;

time ( &curtime ) ; //retrieves current time &

stores in curtime

printf ( "\nCurrent Date & Time: %s", ctime (

&curtime ) ) ;

}

Q:How do I change the type of cursor and hide a cursor?

A: We can change the cursor type by using function _setcursortype( ). This function can change the cursor type to solid cursor and can even hide a cursor. Following code shows how to change the cursor type and hide cursor.

#include

main( )

{

/* Hide cursor */

_setcursortype ( _NOCURSOR ) ;

/* Change cursor to a solid cursor */

_setcursortype ( _SOLIDCURSOR ) ;

/* Change back to the normal cursor */

_setcursortype ( _NORMALCURSOR ) ;

}

C Interview Questions Part 3

noreply@blogger.com (Anonymous) — Sat, 14 Mar 2009 11:41:00 -0700

Q:The Spawnl( ) function...

A:DOS is a single tasking operating system, thus only one program runs at a time. The Spawnl( ) function provides us with the capability of starting the execution of one program from within another program. The first program is called the parent process and the second program that gets called from within the first program is called a child process. Once the second program starts execution, the first is put on hold until the second program completes execution. The first program is then restarted. The following program demonstrates use of spawnl( ) function.

/* Mult.c */

int main ( int argc, char* argv[ ] )

{

int a[3], i, ret ;

if ( argc < 3 || argc > 3 )

{

printf ( "Too many or Too few arguments..." ) ;

exit ( 0 ) ;

}

for ( i = 1 ; i < argc ; i++ )

a[i] = atoi ( argv[i] ) ;

ret = a[1] * a[2] ;

return ret ;

}

/* Spawn.c */

#include

main( )

{

int val ;

val = spawnl ( P_WAIT, "C:\\Mult.exe", "3", "10",

"20", NULL ) ;

printf ( "\nReturned value is: %d", val ) ;

}

Here, there are two programs. The program 'Mult.exe' works as a child process whereas 'Spawn.exe' works as a parent process. On execution of 'Spawn.exe' it invokes 'Mult.exe' and passes the command-line arguments to it.'Mult.exe' in turn on execution, calculates the product of 10 and 20 and returns the value to val in 'Spawn.exe'. In our call to spawnl( ) function, we have passed 6 parameters, P_WAIT as the mode of execution, path of '.exe' file to run as child process, total number of arguments to be passed to the child process, list of command line arguments and NULL. P_WAIT will cause our application to freeze execution until the child process has completed its execution.This parameter needs to be passed as the default parameter if you are working under DOS. under other operating systems that support multitasking, this parameter can be P_NOWAIT or P_OVERLAY. P_NOWAIT will cause the parent process to execute along with the child process, P_OVERLAY will load the child process on top of the parent process in the memory.

C Interview Questions Part 2

noreply@blogger.com (Anonymous) — Fri, 27 Feb 2009 11:39:00 -0800

Q:What will be the output of the following code?

void main ()

{ int i = 0 , a[3] ;

a[i] = i++;

printf (“%d",a[i]) ;

}

A: The output for the above code would be a garbage value. In the statement a[i] = i++; the value of the variable i would get assigned first to a[i] i.e. a[0] and then the value of i would get incremented by 1. Since a[i] i.e. a[1] has not been initialized, a[i] will have a garbage value.

Q:How do I know how many elements an array can hold?

A: The amount of memory an array can consume depends on the data type of an array. In DOS environment, the amount of memory an array can consume depends on the current memory model (i.e. Tiny, Small, Large, Huge, etc.). In general an array cannot consume more than 64 kb. Consider following program, which shows the maximum number of elements an array of type int, float and char can have in case of Small memory model.

main( )

{

int i[32767] ;

float f[16383] ;

char s[65535] ;

}

Q:How do I write code that reads data at memory location specified by segment and offset?

A: Use peekb( ) function. This function returns byte(s) read from specific segment and offset locations in memory. The following program illustrates use of this function. In this program from VDU memory we have read characters and its attributes of the first row. The information stored in file is then further read and displayed using peek( ) function.

#include

main( )

{

char far *scr = 0xB8000000 ;

FILE *fp ;

int offset ;

char ch ;

if ( ( fp = fopen ( "scr.dat", "wb" ) ) == NULL )

{

printf ( "\nUnable to open file" ) ;

exit( ) ;

}

// reads and writes to file

for ( offset = 0 ; offset < 160 ; offset++ )

fprintf ( fp, "%c", peekb ( scr, offset ) ) ;

fclose ( fp ) ;

if ( ( fp = fopen ( "scr.dat", "rb" ) ) == NULL )

{

printf ( "\nUnable to open file" ) ;

exit( ) ;

}

// reads and writes to file

for ( offset = 0 ; offset < 160 ; offset++ )

{

fscanf ( fp, "%c", &ch ) ;

printf ( "%c", ch ) ;

}

fclose ( fp ) ;

}

C Interview Questions Part 1

noreply@blogger.com (Anonymous) — Wed, 4 Feb 2009 11:35:00 -0800

Q: In printf() Function- What is the difference between "printf(...)" and "sprintf(...)"?

A: sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device.

Q:Compilation How to reduce a final size of executable?

A:Size of the final executable can be reduced using dynamic linking for libraries.

Q:Linked Lists -- Can you tell me how to check whether a linked list is circular?

A: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 ("circular");

}

If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, its either 1 or 2 jumps until they meet.

Q:string Processing --- Write out a function that prints out all the permutations of a string. For example, abc would give you abc, acb, bac, bca, cab, cba.

A:void PrintPermu (char *sBegin, char* sRest) {

int iLoop;

char cTmp;

char cFLetter[1];

char *sNewBegin;

char *sCur;

int iLen;

static int iCount;

iLen = strlen(sRest);

if (iLen == 2) {

iCount++;

printf("%d: %s%s\n",iCount,sBegin,sRest);

iCount++;

printf("%d: %s%c%c\n",iCount,sBegin,sRest[1],sRest[0]);

return;

} else if (iLen == 1) {

iCount++;

printf("%d: %s%s\n", iCount, sBegin, sRest);

return;

} else {

// swap the first character of sRest with each of

// the remaining chars recursively call debug print

sCur = (char*)malloc(iLen);

sNewBegin = (char*)malloc(iLen);

for (iLoop = 0; iLoop <>

strcpy(sCur, sRest);

strcpy(sNewBegin, sBegin);

cTmp = sCur[iLoop];

sCur[iLoop] = sCur[0];

sCur[0] = cTmp;

sprintf(cFLetter, "%c", sCur[0]);

strcat(sNewBegin, cFLetter);

debugprint(sNewBegin, sCur+1);

}

void main() {

char s[255];

char sIn[255];

printf("\nEnter a string:");

scanf("%s%*c",sIn);

memset(s,0,255);

PrintPermu(s, sIn);

}