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Language in C Interview Questions and Answers

Ques 6. How do I compare character data stored at two different memory locations?

Ans. 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 <mem.h>

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" ) ;
}

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Ques 7. The Spawnl( ) function...

Ans. 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 <process.h>
#include <stdio.h>

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.
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Ques 8. Are the following two statements identical?

char str[6] = "Kicit" ;
char *str = "Kicit" ;
Ans. 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.
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Ques 9. Is the following code fragment correct?

const int x = 10 ;
int arr[x] ;
Ans. 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.
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Ques 10. How do I write code to retrieve current date and time from the system and display it as a string?

Ans. 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 <sys\types.h>

void main( )
{
time_t curtime ;
char ctm[50] ;

time ( &curtime ) ; //retrieves current time &
stores in curtime
printf ( "\nCurrent Date & Time: %s", ctime (
&curtime ) ) ;
}

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char *str = "Kicit" ;
4) Is the following code fragment correct?

const int x = 10 ;
int arr[x] ;
5) How do I write code to retrieve current date and time from the system and display it as a string?

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