C Programming: C pointer question

C pointers interview questions and answers

It is frequently asked technical objective types multiple choice questions of placement in c programming language

Note: Linux GCC compilers and Visual C++ compiler doesn't support far and huge pointers.

What will be output of following program?

#include<stdio.h>

int main(){

int a = 320;

char *ptr;

ptr =( char *)&a;

printf("%d ",*ptr);

return 0;

}

(A) 2
(B) 320
(C) 64
(D) Compilation error
(E) None of above

Output : (C)

Explanation:

Turbo C++ 3.0: 64

Turbo C ++4.5: 64

Linux GCC: 64

Visual C++: 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 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 which color is green and Decimal value is 64.

What will be output of following program?

#include<stdio.h>

#include<conio.h>

int main(){

void (*p)();

int (*q)();

int (*r)();

p = clrscr;

q = getch;

r = puts;

(*p)();

(*r)("ctechnotips.blogspot.com");

(*q)();
return 0;

}

(A) NULL
(B) ctechnotips.blogspot.com
(C) c
(D) Compilation error
(E) None of above

Output : (B)

Explanation:

Turbo C++ 3.0: ctechnotips.blogspot.com

Turbo C ++4.5: ctechnotips.blogspot.com

Linux GCC: Compilation error

Visual C++: Compilation error

p is pointer to function whose parameter is void and return type is also void. r and q is pointer to function whose parameter is void and return type is int . So they can hold the address of such function.

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;

}

(A) Address, Address, 3
(B) Address, 3, 3
(C) 3, 3, 3
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0: Address, Address, 3

Turbo C ++4.5: Address, Address, Address

Linux GCC: Address, Address, 3

Visual C++: Address, Address, 3

Memory representation

Here 6024, 8085, 9091 is any arbitrary address, it may be different.

Value of k is content of k in memory which is 8085

Value of *k means content of memory location which address k keeps.

k keeps address 8085 .

Content of at memory location 8085 is 6024

In the same way **k will equal to 3.

Short cut way to calculate:

Rule: * and & always cancel to each other

i.e. *&a = a

So *k = *(&j) since k = &j

*&j = j = 6024

And

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

What will be output of following program?

#include<stdio.h>

int main(){

char far *p =(char far *)0x55550005;

char far *q =(char far *)0x53332225;

*p = 80;

(*p)++;

printf("%d",*q);

return 0;

}

(A) 80
(B) 81
(C) 82
(D) Compilation error
(E) None of above

Output : (B)

Explanation:

Turbo C++ 3.0: 81

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

Far address of p and q are representing same physical address.

Physical address of 0x55550005 = (0x5555) * (0x10) + (0x0005) = 0x55555

Physical address of 0x53332225 = (0x5333 * 0x10) + (0x2225) = 0x55555

*p = 80, means content at memory location 0x55555 is assigning value 25

(*p)++ means increase the content by one at memory location 0x5555 so now content at memory location 0x55555 is 81

*q also means content at memory location 0x55555 which is 26

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;

}

(A) c questions
(B) c (null)
(C) (null) (null)
(D) Compilation error
(E) None of above

Output : (C)

Explanation:

Turbo C++ 3.0: (null) (null)

Turbo C ++4.5: Run time error

Linux GCC: Run time error

Visual C++: 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 huge *a =(int huge *)0x59990005;

int huge *b =(int huge *)0x59980015;

if(a == b)

printf("power of pointer");

else

printf("power of c");

return 0;

}

(A) power of pointer
(B) power of c
(C) power of cpower of c
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0: power of pointer

Turbo C ++4.5: power of c

Linux GCC: Compilation error

Visual C++: Compilation error

Here we are performing relational operation between two huge addresses. So first of all both a and b will normalize as:

a= (0x5999)* (0x10) + (0x0005) =0x9990+0x0005=0x9995

b= (0x5998)* (0x10) + (0x0015) =0x9980+0x0015=0x9995

Here both huge addresses are representing same physical address. So a==b is true.

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main(){

int far *p;

p=&a;

printf("%d ",*p);

return 0;

}

(A) 25
(B) 4
(C) Address
(D) Compilation error
(E) None of above

Output : (D)

Explanation:

Turbo C++ 3.0: Compilation error

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main(){

char far *p,*q;

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

return 0;

}

(A) 2 2
(B) 4 4
(C) 4 2
(D) 2 4
(E) None of above

Output : (C)

Explanation:

Turbo C++ 3.0: 4 4

Turbo C ++4.5: 4 4

Linux GCC: Compilation error

Visual C++: Compilation error

p is far pointer which size is 4 byte.

By default q is near pointer which size is 2 byte.

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;

}

(A) 10
(B) Address
(C) 2
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0: 10

Turbo C ++4.5: 10

Linux GCC: 10

Visual C++: 10

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

10.

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main(){

int register a;

scanf("%d",&a);

printf("%d",a);

return 0;

}

//if a=25

(A) 25
(B) Address
(C) 0
(D) Compilation error
(E) None of above

Output : (D)

Explanation:

Turbo C++ 3.0: Compilation error

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

11.

What will be output of following program?

#include<stdio.h>

int main(){

char arr[10];

arr = "world";

printf("%s",arr);

return 0;

}

(A) world
(B) w
(C) Null
(D) Compilation error
(E) None of above

Output : (D)

Explanation:

Turbo C++ 3.0: Compilation error

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

Compilation error Lvalue required

Array name is constant pointer and we cannot assign any value in constant data type after declaration.

12.

What will be output of following program?

#include<stdio.h>

#include<string.h>

int main(){

int a,b,c,d;

char *p = ( char *)0;

int *q = ( int *q)0;

float *r = ( float *)0;

double *s = 0;

a = (int)(p+1);

b = (int)(q+1);

c = (int)(r+1);

d = (int)(s+1);

printf("%d %d %d %d",a,b,c,d);
return 0;

}

(A) 2 2 2 2
(B) 1 2 4 8
(C) 1 2 2 4
(D) Compilation error
(E) None of above

Output : (B)

Explanation:

Turbo C++ 3.0: 1 2 4 8

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

Address + 1 = next address

Since initial address of all data type is zero. So its

next address will be size of data type.

13.

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;

}

(A) 1
(B) 5
(C) -5
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0: 1

Turbo C ++4.5: 1

Linux GCC: 1

Visual C++: 2

Difference of two same type of pointer is always one.

14.

What will be output of following program?

#include<stdio.h>

unsigned long int (* avg())[3]{

static unsigned long int arr[3] = {1,2,3};

return &arr;

}

int main(){

unsigned long int (*ptr)[3];

ptr = avg();

printf("%d" , *(*ptr+2));

return 0;

}

(A) 1
(B) 2
(C) 3
(D) Compilation error
(E) None of above

Output : (C)

Explanation:

Turbo C++ 3.0: 3

Turbo C ++4.5: 3

Linux GCC: 3

Visual C++: 3

15.

What will be output of following program?

#include<stdio.h>

int main(){

int * p , b;

b = sizeof(p);

printf("%d" , b);
return 0;

}

(A) 2
(B) 4
(C) 8
(D) Compilation error
(E) None of above

Output : (E)

Explanation:

Turbo C++ 3.0: 2 or 4

Turbo C ++4.5: 2 or 4

Linux GCC: 4

Visual C++: 4

since in this question it has not written p is which type of pointer. So its output will depend upon which memory model has selected. Default memory model is small.

16.

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;

}

(A) 5 5
(B) Address Address
(C) 5 Address
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0: 5 5

Turbo C ++4.5: 5 5

Linux GCC: 5 5

Visual C++: 5 5

17.

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;

}

(A) 5 Address
(B) Address Address
(C) Address 5
(D) Compilation error
(E) None of above

Output : (B)

Explanation:

Turbo C++ 3.0: Address Address

Turbo C ++4.5: Address Address

Linux GCC: Address Address

Visual C++: Address Address

Since * and & always cancel to each other.

i.e. *&a = a

so *&p = p which store address of integer i

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

= &(*&i)

= &i

So second output is also address of i

18.

What will be output of following program?

#include<stdio.h>

int main(){

int i = 100;

printf("value of i : %d addresss of i : %u",i,&i);

i++;

printf("\nvalue of i : %d addresss of i : %u",i,&i);

return 0;

}

(A) value of i : 100 addresss of i : Address value of i : 101 addresss of i : Address
(B) value of i : 100 addresss of i : Address value of i : 100 addresss of i : Address
(C) value of i : 101 addresss of i : Address value of i : 101 addresss of i : Address
(D) Compilation error
(E) None of above

Output : (A)

Explanation:

Turbo C++ 3.0:

value of i : 100 addresss of i : Address

value of i : 101 addresss of i : Address

Turbo C ++4.5:

value of i : 100 addresss of i : Address

value of i : 101 addresss of i : Address

Linux GCC:

value of i : 100 addresss of i : Address

value of i : 101 addresss of i : Address

Visual C++:

value of i : 100 addresss of i : Address

value of i : 101 addresss of i : Address

Within the scope of any variable, value of variable may change but its address will never change in any modification of variable.

19.

What will be output of following program?

#include<stdio.h>

int main(){

char far *p =(char far *)0x55550005;

char far *q =(char far *)0x53332225;

*p = 25;

(*p)++;

printf("%d",*q);

return 0;

}

(A) 25
(B) Address
(C) Garbage
(D) Compilation error
(E)None of above

Output : (E)

Explanation:

Turbo C++ 3.0: 26

Turbo C ++4.5: Compilation error

Linux GCC: Compilation error

Visual C++: Compilation error

Far address of p and q are representing same physical address. Physical address of

0x55550005 = 0x5555 * ox10 + ox0005 = 0x55555

Physical address of

0x53332225 = 0x5333 * 0x10 + ox2225 = 0x55555

*p = 25, means content at memory location 0x55555 is assigning value 25

(*p)++ means to increase the content by one at memory the location 0x5555 so now content of memory location at 0x55555 is 26

*q also means content at memory location 0x55555 which is 26

20.

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;

}

(A) 3 Address 3
(B) 3 Address Address
(C) 3 3 3
(D) Compilation error
(E) None of above

Output : (B)

Explanation:

Turbo C++ 3.0: 3 Address Address

Turbo C ++4.5: 3 Address Address

Linux GCC: 3 Address Address

Visual C++: 3 Address Address

Here 6024, 8085, 9091 is any arbitrary address, it may be different.

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