C Interview Questions And Answers

Q:Which bit wise operator is suitable for checking whether a particular bit is on or off?
Ans:The bitwise AND operator. Here is an example:enum {
KBit0 = 1,
KBit1,
…
KBit31,
};

if ( some_int & KBit24 )
printf ( “Bit number 24 is ON\n” );
else
printf ( “Bit number 24 is OFF\n” );

Q:Which bit wise operator is suitable for turning off a particular bit in a number?
Ans:The bitwise AND operator, again. In the following code snippet, the bit number 24 is reset to zero.
some_int = some_int & ~KBit24;

Q:Which bit wise operator is suitable for putting on a particular bit in a number?
Ans:The bitwise OR operator. In the following code snippet, the bit number 24 is turned ON:
some_int = some_int | KBit24;

Q:Does there exist any other function which can be used to convert an integer or a float to a string?
Ans:Some implementations provide a nonstandard function called itoa(), which converts an integer to string.

#include

char *itoa(int value, char *string, int radix);

DESCRIPTION
The itoa() function constructs a string representation of an integer.

PARAMETERS
value:
Is the integer to be converted to string representation.

string:
Points to the buffer that is to hold resulting string.
The resulting string may be as long as seventeen bytes.

radix:
Is the base of the number; must be in the range 2 - 36.

A portable solution exists. One can use sprintf():

char s[SOME_CONST];
int i = 10;
float f = 10.20;

sprintf ( s, “%d %f\n”, i, f );

Q:Why does malloc(0) return valid memory address ? What's the use ?
Ans:malloc(0) does not return a non-NULL under every implementation.
An implementation is free to behave in a manner it finds
suitable, if the allocation size requested is zero. The
implmentation may choose any of the following actions:

* A null pointer is returned.
* The behavior is same as if a space of non-zero size
was requested. In this case, the usage of return
value yields to undefined-behavior.

Q:Notice, however, that if the implementation returns a non-NULL value for a request of a zero-length space, a pointer to object of ZERO length is returned! Think, how an object of zero size should be represented?
Ans:For implementations that return non-NULL values, a typical usage is as follows:
void
func ( void )
{
int *p; /* p is a one-dimensional array,
whose size will vary during the
the lifetime of the program */
size_t c;
p = malloc(0); /* initial allocation */
if (!p)
{
perror (”FAILURE” );
return;
}
/* … */
while (1)
{
c = (size_t) … ; /* Calculate allocation size */
p = realloc ( p, c * sizeof *p );
/* use p, or break from the loop */
/* … */
}
return;
}

Notice that this program is not portable, since an implementation
is free to return NULL for a malloc(0) request, as the C Standard
does not support zero-sized objects.