C Interview Questions And Answers - Part 5.

What will be output of the following program?

#include<stdio.h>

int main() {

int a = 2, b = 7, c = 10;

c = a == b;

printf("%d",c);

return 0;

}

Output: 0

== is a relational operator which returns only two values.

0: If a == b is false
1: If a == b is true

Since a = 2 and b = 7, so a == b is false, thus c = 0

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main() {

char *ptr1 = NULL;

char *ptr2 = 0;

strcpy(ptr1," c");

strcpy(ptr2,"questions");

printf("\n%s %s",ptr1,ptr2);

return 0;

}

Output: Run time error. 
We cannot assign any string constant in null pointer by strcpy function.

What will be output of following program?

#include<stdio.h>

int main() {

int * p , b;

b = sizeof(p);

printf("%d" , b);

return 0;

}

Output: 4

What will be output of following program?

#include<stdio.h>

int main() {

int i = 5;

int *p;

p = &i;

printf(" %u %u", *&p , &*p);

return 0;

}

Output: address address

* and & always cancel to each other, 
i.e. *&a = a, so *&p = p which store address of integer i. 

Again, &*p = &*(&i)  //since p = &i 
= &(*&i)

= &i

Hence second output is also address of i. 

What will be output of following program?

#include<stdio.h>

int main() {

int i = 3;

int *j;

int **k;

j=&i;

k=&j;

printf("%u %u %d ",k,*k,**k);

return 0;

}

Output: address address 3

Here 6024, 8085, 9091 are arbitrary addresses. The value of k is the content of k in memory which is 8085. 

The value of *k means the content of memory location which address k keeps. k keeps address 8085. The content of at memory location 8085 is 6024. In the same way **k will equal to 3. 

Easy way to calculate: Rule: * and & always cancel to each other i.e. *&a = a, so

*k = *(&j)         // since k = &j

*&j = j = 6024

**k = **(&j) = *(*&j) = *j = *(&i) = *&i = i = 3

What will be output of following program?

#include<stdio.h> 

int main() {

int i = 3;

int *j;

int **k;

j = &i;

k = &j;

printf("%u %u %u",i,j,k);

return 0;

}

Output: 3 address address

What will be output of following program?

#include<stdio.h>

int main() {

int i = 5 , j;

int *p , *q;

p = &i;

q = &j;

j = 5;

printf("%d %d",*p,*q);

return 0;

}

Output: 5 5

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main() {

int a = 5, b = 10, c;

int *p = &a, *q = &b;

c = p - q;

printf("%d", c);

return 0;

}

Output: 1

The difference of two same type of pointer is always one.

What will be output of following program?

#include<stdio.h>

int main() {

int a = 320;

char *ptr;              // use int *ptr; output is 320

ptr =( char *)&a;

printf("%d ",*ptr);

return 0;

}

Output: 64

As we know “int” is two-byte data byte while “char” is one-byte data byte. “char” pointer can keep the address one byte at a time.

Binary value of 320 is 00000001 01000000 (In 16 bit)

Memory representation of int a = 320 is:

So ptr is pointing only first 8 bit and its decimal value is 64.

What will be output of following program?

#include<stdio.h>

int main() {

int a = 10;

void *p = &a;

int *ptr = p;

printf("%u",*ptr);

return 0;

}

Output: 10

void pointer can hold the address of any data type without type casting. Any pointer can hold void pointer without type casting.