C Objective Questions and Answers

C Objective Questions and Answers
C Technical Interview Questions and Answers
-----------------------------------------------------------------------------------------------------------




50.

How do I print a floating-point number with higher precision say 23.34568734 with only precision up to two decimal places?

Ans: This can be achieved through the use of suppression char '*' in the format string of printf( ) as shown in the following program.
main( )
{
int i = 2 ;
float f = 23.34568734 ;
printf ( "%.*f", i, f ) ;
}
The output of the above program would be 23.35.

-------------------------------------------------------------------------------------------------
51.
Are the expressions *ptr++ and ++*ptr same?

Ans: No. *ptr++ increments the pointer and not the value pointed by it, whereas ++*ptr increments the value being pointed to by ptr.

-------------------------------------------------------------------------------------------------

52.
strpbrk( )

The function strpbrk( ) takes two strings as parameters. It scans the first string, to find, the first occurrence of any character appearing in the second string. The function returns a pointer to the first occurrence of the character it found in the first string. The following program demonstrates the use of string function strpbrk( ).

#include <string.h>
main( )
{
char *str1 = "Hello!" ;
char *str2 = "Better" ;
char *p ;
p = strpbrk ( str1, str2 ) ;

if ( p )
printf ( "The first character found in str1 is %c", *p ) ;
else
printf ( "The character not found" ) ;
}
The output of the above program would be the first character found in str1 is e


53.

Can we convert an unsigned long integer value to a string?

Ans: The function ultoa( ) can be used to convert an unsigned long integer value to a string. This function takes three arguments, first the value that is to be converted, second the base address of the buffer in which the converted number has to be stored (with a string terminating null character '\0') and the last argument specifies the base to be used in converting the value. Following example demonstrates the use of this function.

#include <stdlib.h>
void main( )
{
unsigned long ul = 3234567231L ;
char str[25] ;

ultoa ( ul, str, 10 ) ;
printf ( "str = %s unsigned long = %lu\n", str, ul ) ;
}


-------------------------------------------------------------------------------------------------
54.
ceil( ) and floor( )

The math function ceil( ) takes a double value as an argument. This function finds the smallest possible integer to which the given number can be rounded up. Similarly, floor( ) being a math function, takes a double value as an argument and returns the largest possible integer to which the given double value can be rounded down. The following program demonstrates the use of both the functions.

#include <math.h>
void main( )
{
double no = 1437.23167 ;
double down, up ;

down = floor ( no ) ;
up = ceil ( no ) ;

printf ( "The original number %7.5lf\n", no ) ;
printf ( "The number rounded down %7.5lf\n", down ) ;
printf ( "The number rounded up %7.5lf\n", up ) ;
}

The output of this program would be,
The original number 1437.23167
The number rounded down 1437.00000
The number rounded up 1438.00000


-------------------------------------------------------------------------------------------------
55.

How do I use function ecvt( ) in a program?

Ans: The function ecvt( ) converts a floating-point value to a null terminated string. This function takes four arguments, such as, the value to be converted to string, the number of digits to be converted to string, and two integer pointers. The two-integer pointer stores the position of the decimal point (relative to the string) and the sign of the number, respectively. If the value in a variable, used to store sign is 0, then the number is positive and, if it is non-zero, then the number is negative. The function returns a pointer to the string containing digits. Following program demonstrates the use of this function.

#include <stdlib.h>
main( )
{
char *str ;
double val ;
int dec, sign ;
int ndig = 4 ;

val = 22 ;
str = ecvt ( val, ndig, &dec, &sign ) ;
printf ( "string = %s dec = %d sign = %d\n", str, dec, sign ) ;

val = -345.67 ;
ndig = 8 ;
str = ecvt ( val, ndig, &dec, &sign ) ;
printf ( "string = %s dec = %d sign = %d\n", str, dec, sign ) ;

// number with a scientific notation
val = 3.546712e5 ;
ndig = 5 ;
str = ecvt ( val, ndig, &dec, &sign ) ;
printf ( "string = %s dec = %d sign = %d\n", str, dec, sign ) ;
}

The output of this program would be

string = 2200 dec = 2 sign = 0
string = 34567000 dec = 3 sign = 1
string = 35467 dec = 6 sign = 0


-------------------------------------------------------------------------------------------------

56.

How to run DIR command programmatically?

Ans: We can use the system( ) function to execute the DIR command along with its options. Following program shows how this can be achieved:

// mydir.c

main ( int argc, char *argv[ ] )
{
char str[30] ;

if ( argc < 2 )
exit ( 0 ) ;

sprintf ( str, "dir %s %s", argv[1], argv[2] ) ;
system ( str ) ;
}

If we run the executable file of this program at command prompt passing the command line arguments as follows:

> mydir abc.c /s

This will search the file 'abc.c' in the current directory.
-------------------------------------------------------------------------------------------------
57.

Suppose I have a structure having fields name, age, salary and have passed address of age to a function fun( ). How I can access the other member of the structure using the address of age?
Ans:
struct emp
{
char name[20] ;
int age ;
float salary ;
} ;
main( )
{
struct emp e ;
printf ( "\nEnter name: " ) ;
scanf ( "%s", e.name ) ;
printf ( "\nEnter age: " ) ;
scanf ( "%d", &e.age ) ;
printf ( "\nEnter salary: " ) ;
scanf ( "%f", &e.salary ) ;
fun ( &e.age ) ;
}
fun ( int *p )
{
struct emp *q ;
int offset ;
offset = ( char * ) ( & ( ( struct emp * ) 0 ) -> age ) - ( char * ) ( (
struct emp* ) 0 ) ;
q = ( struct emp * ) ( ( char * ) p - offset ) ;
printf ( "\nname: %s", q -> name ) ;
printf ( "\nage: %d", q -> age ) ;
printf ( "\nsalary: %f", q -> salary ) ;
}


58.

How to restrict the program's output to a specific screen region?

Ans: A C function window( ) can be used to restrict the screen output to a specific region. The window( ) function defines a text-mode window. The parameters passed to this function defines the upper-left and lower-right corner of the region within which you want the output. In the following program, the string 'Hello!' gets printed within the specified region. To print the string we must use cprintf( ) function which prints directly on the text-mode window.

#include <conio.h>
main( )
{
int i, j ;

window ( 20, 8, 60, 17 ) ;
for ( i = 0 ; i < 8 ; i++ )
for ( j = 0 ; j < 10 ; j++ )
cprintf ( "Hello!" ) ;
}

-------------------------------------------------------------------------------------------------
59.

Sometimes you need to prompt the user for a password. When the user types in the password, the characters the user enters should not appear on the screen. A standard library function getpass( ) can be used to perform such function. Maximum number of characters that can be entered as password is 8.

main( )
{
char *pwd ;

pwd = getpass ( "Enter Password" ) ;

if ( strcmp ( pwd, "orgcity" ) )
printf ( "\nPassword %s is incorrect", pwd ) ;
else
printf ( "\nCorrect Password" ) ;
}


-------------------------------------------------------------------------------------------------
60.
How to obtain the current drive through C ?

Ans: We can use the function _getdrive( ) to obtain the current drive. The _getdrive( ) function uses DOS function 0X19 to get the current drive number

#include <direct.h>
main( )
{
int disk ;
disk = _getdrive( ) + 'A' - 1 ;
printf ( "The current drive is: %c\n", disk ) ;
}


-------------------------------------------------------------------------------------------------
61.

How come the output for both the programs is different when the logic is same?

main( )
{
int i, j ;

for ( i = 1, j = 1 ; i <= 5, j <= 100 ; i++, j++ )
{
gotoxy ( 1, 1, ) ;
printf ( "%d %d", i, j ) ;
}
}

main( )
{
int i, j ;

for ( i =1, j = 1; j <= 100, i <= 5; i++, j++ )
{
gotoxy ( 1, 1 ) ;
printf ( "%d %d", i, j ) ;
}
}

Output -> 5 5
Even if logic of both the programs is same the output of the first program comes out to be 100, 100, but of the second program it is 5, 5. The comma operator plays a vital role inside the for loop. It always considers the value of the latest variable. So, at the time of testing the condition in for loop, the value of j will be considered in the first program and value of i in the second.


-------------------------------------------------------------------------------------------------
62.
Can we get the x and y coordinate of the current cursor position ?

Ans : The function wherex( ) and wherey( ) returns the x-coordinate and y-coordinate of the current cursor position respectively. Both the functions return an integer value. The value returned by wherex( ) is the horizontal position of cursor and the value returned by wherey( ) is the vertical position of the cursor. Following program shows how to use the wherex( ) and wherey( ) functions.

#include <conio.h>
main( )
{
printf ( "Just\n To\n Test\n Where\n the cursor\n goes" ) ;

printf ( "Current location is X: %d Y: %d\n", wherex( ), wherey( ) ) ;
}


63.
How do I programmatically delete lines in the text window?

Ans: While writing programs that perform screen-based I/O, you may want to-delete the current line's contents, moving one line up, all of the output that follows. In such cases a function called delline( ) can be used. Following code snippet illustrates the use of function delline( ).

#include <conio.h>
main( )
{
int i ;
clrscr( ) ;

for ( i = 0; i <= 23; i++ )
printf ( "Line %d\r\n", i ) ;

printf ( "Press a key to continue : " ) ;
getch( ) ;

gotoxy ( 2, 6 ) ;

for ( i = 6; i <= 12; i++ )
delline( ) ;

getch( ) ;
}


-------------------------------------------------------------------------------------------------
64.

How do I get the time elapsed between two function calls ?

Ans: The function difftime( ) finds the difference between two times. It calculates the elapsed time in seconds and returns the difference between two times as a double value.

#include <time.h>
#include <stdio.h>
#include <dos.h>

main( )
{
int a[] = { 2, -34, 56, 78, 112, 33, -7, 11, 45, 29, 6 } ;
int s ;
time_t t1, t2 ; // time_t defines the value used for time function

s = sizeof ( a ) / 2 ;
t1 = time ( NULL ) ;
sel_sort ( a, s ) ; // sort array by selection sort
bub_sort ( a, s ) ; // sort array by bubble sort method
t2 = time ( NULL ) ;
printf ( "\nThe difference between two function calls is %f", difftime (
t2, t1 ) ) ;
}

In the above program we have called difftime( ) function that returns the time elapsed from t1 to t2.


-------------------------------------------------------------------------------------------------
65.

How do I use swab( ) in my program ?

Ans: The function swab( ) swaps the adjacent bytes of memory. It copies the bytes from source string to the target string, provided that the number of characters in the source string is even. While copying, it swaps the bytes which are then assigned to the target string.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

main ( )
{
char *str1 = "hS eesll snsiasl not eh es as oher " ;
char *str2 ;
clrscr( ) ;
swab ( str1, str2, strlen ( str1 ) ) ;
printf ( "The target string is : %s\n", str2 ) ; // output -- She sells
snails on the sea shore
getch( ) ;
}

-------------------------------------------------------------------------------------------------
66.

Turbo C provides various command line compiler options which we can use through TCC. The compiler options include : displaying specific warning messages, generating 8087 hardware instructions, using a filename for generating assembly code, etc. Instead of compiler options being executed at command line we can use these compiler options in our program. This can be achieved using #pragma options. We can use various flags with #pragma options to use the compiler options. All these flags are available in turbo C's online help.
-------------------------------------------------------------------------------------------------
67.

I have an array declared in file 'F1.C' as,
int a[ ] = { 1, 2, 3, 4, 5, 6 } ;
and used in the file 'F2.C' as,
extern int a[ ] ;

In the file F2.C, why sizeof doesn't work on the array a[ ]?

Ans: An extern array of unspecified size is an incomplete type. You cannot apply sizeof to it, because sizeof operates during compile time and it is unable to learn the size of an array that is defined in another file. You have three ways to resolve this problem:
1. In file 'F1.C' define as,
int a[ ] = { 1, 2, 3, 4, 5, 6 } ;
int size_a = sizeof ( a ) ;
and in file F2.C declare as,
extern int a[ ] ;
extern int size_a ;

2. In file 'F1.H' define,

#define ARR_SIZ 6
In file F1.C declare as,
#include "F1.H"
int a[ ARR_SIZ ] ;
and in file F2.C declare as,
#include "F1.H"
extern int a[ ARR_SIZ ] ;
3. In file 'F1.C' define as,
int a[ ] = { 1, 2, 3, 4, 5, 6, -1 } ;

and in file 'F2.C' declare as,

extern int a[ ] ;
Here the element -1 is used as a sentinel value, so the code can
understand the end without any explicit size.

68.

How to delete a line from text displayed on the screen?

Ans: Sometimes, specially when we are creating a text editor like program we may wish to allow user to delete a line. We can do so by using two functions namely clreol( ) and delline( ). The clreol( ) function deletes the line from the current cursor position to the end of line. The delline() function deletes the entire line at the current cursor position and
moves up the following line. Following program shows how to use these functions.

#include <conio.h>

main( )
{
int i ;

for ( i = 1 ; i <= 20 ; i++ )
printf ( "This is Line %d\n", i ) ;

getch( ) ;
gotoxy ( 1, 7 ) ;
clreol( ) ;

getch( ) ;
gotoxy ( 1, 12 ) ;
delline( ) ;

getch( ) ;
}


-------------------------------------------------------------------------------------------------
69.
How do I programmatically insert lines in the text window?

Ans: We can insert a blank line in the text window using the insline( ) function. This function inserts line at current cursor position. While doing so, it shifts down the lines that are below the newly inserted line.

#include <conio.h>
void main( )
{
printf ( "The little snail was slowly moving up. She wanted\r\n" ) ;
printf ( "to reach the top of the tree. It was chilly\r\n" ) ;
printf ( "winter season. Most of the animals were resting in\r\n" ) ;
printf ( "their nests as there was a heavy snow fall.\r\n" ) ;
printf ( "\r\nPress any key to continue:" ) ;

gotoxy ( 10, 2 ) ;
getch( ) ;
insline( ) ;
getch( ) ;
}


-------------------------------------------------------
ANish