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C Bitwise Operators - Aptitude Questions and Answers

C programming Bitwise Operators Aptitude Questions and Answers: In this section you will find C Aptitude Questions and Answers on Bitwise Operators like Bitwise OR (|), Bitwise AND (&), Bitwise NOT (!).

1) Which is not a bitwise operator?

Answer & Explanation

2) Predict the output of following program.

#include <stdio.h>

int main()
{
	int a=10;
	int b=2;
	int c;
	
	c=(a & b);
	printf("c= %d",c);
	
	return 0;
}

Answer & Explanation

Correct answer: 3
c= 2

Bitwise AND (&), It does AND on every bits of two numbers. The result of AND is 1 only if both bits are 1.

    a=10 //0000 1010
    b=2 //0000 0010
    Doing bitwise AND
    0000 0010// 2

For details on bitwise operator refer to Bitwise Operators and their working with Examples in C

3) Predict the output of following program.

#include <stdio.h>

#define MOBILE  0x01
#define LAPPY   0x02

int main()
{
	unsigned char  item=0x00;

	item |=MOBILE;
	item |=LAPPY;

	printf("I have purchased ...:");
	if(item & MOBILE){
		printf("Mobile, ");
	}
	if(item & LAPPY){
		printf("Lappy");
	}

	return 1;
}

Answer & Explanation

4) Predict the output of following program.

#include <stdio.h>

int main()
{
	char var=0x04;

	var = var | 0x04;
	printf("%d,",var);
	var |= 0x01;
	printf("%d",var);
	
	return 0;
}

Answer & Explanation

5) Predict the output of following program.

#include <stdio.h>

int main()
{
	char flag=0x0f;

	flag &= ~0x02;
	printf("%d",flag);

	return 0;
}

Answer & Explanation

Correct answer: 1
13

Consider the expression:

    flag = 0x0f //0000 1111
    flag &= ~0x02
    flag = flag & (~0x02) //since ~ has precedence over ‘&’ operator
    0x02 = 0000 0010
    ~0x02 = 1111 1101
    flag & ~0x02
    = 0000 1111 & 1111 1101
    = 0000 1101
    = 0x0D

But since the placeholder in printf is %d, it prints the decimal value 13.

6) Consider the given statement:

int x = 10 ^ 2

What will be the value of x?

Answer & Explanation

Correct answer: 4
8

XOR operator (^) copies bit(s), if one operand has 1 and other has 0, consider the given truth table:

a       b       (a^b)
_______________________

0       0       0
0       1       1
1       0       1
1       1       0

Here, binary of 10 is "1010" and binary of 2 is "0010", then the result of statement (10 ^ 2) will be "1000", which is equivalent to 8 in decimal.

7) Predict the output of following program.

#include <stdio.h>

int main()
{
    int x=10;
    
    x &= ~2;
    printf("x= %d",x);
    
    return 0;
}

Answer & Explanation

Correct answer: 2
x= 8

Consider the explanation:

    x =10//0000 1010
    x &= ~2
    x = x & (~2) //since ~ has precedence over ‘&’ operator
    2 = 0000 0010
    ~2 = 1111 1101
    x & ~0x02
    = 0000 1010& 1111 1101
    = 0000 1000
    = 8

The statement x &= ~2; will clear second bit from the value of 10, binary of x is "1010" and the binary of 2 is "0010", thus this statement will clear second bit and returns "1000" that is equivalent to 8 in Decimal.

8) Which Bitwise Operator can be used to check whether a number is EVEN or ODD quickly?

Answer & Explanation

Correct answer: 1
Bitwise AND (&)

Bitwise AND (&) Operator can be used to check whether a number if EVEN or ODD, consider the statement (num & 1), this statement will return 1 if first bit of the number is High (1) else it will return 0. All ODD numbers have their firs bit 1 and ODD numbers have 0.

Consider the following program:

#include <stdio.h>

int main()
{
    int count;
    
    for(count=1; count<=10; count+=1)
        if(count & 1)
            printf("%2d is ODD number\n",count);
        else
            printf("%2d is EVEN number\n",count);
    
    return 0;
}

Output

 1 is ODD number
 2 is EVEN number
 3 is ODD number
 4 is EVEN number
 5 is ODD number
 6 is EVEN number
 7 is ODD number
 8 is EVEN number
 9 is ODD number
10 is EVEN number

9) Which statement is suitable to check 3^rd (count from 0) bit is high (set) or not?

Answer & Explanation

Correct answer: 4
Both (1) and (2)

The value of (1<<3) is 8 in Decimal and value of 0x08 is 8 in Decimal, both statements are suitable to check whether 3^rd bit of num is High (set) or not.

Consider this program:

#include <stdio.h>

int main()
{
    int num;
    
    printf("Enter an integer number: ");
    scanf("%d",&num);
    
    if(num & (1<<3))
        printf("3rd bit is High (Set)\n");
    else
        printf("3rd bit is Low\n");
        
    return 0;
}

Output

First run:
Enter an integer number: 15 
3rd bit is High (Set) 

Second run:
Enter an integer number: 7
3rd bit is Low

Binary of 15 is: 1111 & Binary of 7 is: 0111, thus in first case 3^rd bit is high and in second case 3^rd bit is low. [Count from 0]

10) Left shift (<<) and Right shift (>>) operators are equivalent to _____________ by 2.

Choose the correct words...

Answer & Explanation

Correct answer: 1
Multiplication and Division

Left shift by 1 return the multiplication by 2 and Right shift by 1 return the division by 2.

Consider this program:

#include <stdio.h>

int main()
{
    int num;
    
    printf("Enter an integer number: ");
    scanf("%d",&num);
    
    printf("Multiplication by 2 = %d\n", (num<<1));
    printf("Division by 2 = %d\n",(num>>1));
        
    return 0;
}

Output

Enter an integer number: 100
Multiplication by 2 = 200 
Division by 2 = 50

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