C Program to Toggle Bits

Here we’ll see how to write C program to toggle all bits or a particular bit or all but a particular bit of a number.

Toggle All Bits of a Number

We can toggle all bits of a number using NOT (~) bitwise operation. Doing NOT (~) operation on a number toggles all of its bits.

#include <stdio.h>

void binary(unsigned int n)
{
	unsigned int mask = 0x80000000;
    while(mask) {
	  printf("%d", (n&mask)?1:0);
	  mask = mask >> 1;
	}
}

void main()
{
    unsigned int num = 0;

    printf("Enter an integer: ");
    scanf("%d", &num);

    printf("Binary represntation of the input number:\n");
    binary(num);
    
    num = ~num;
    
    printf("\n\nAfter toggling all bits of the number:\n");
    binary(num);
    printf("\n");
}

This program takes an unsigned integer as input and prints the 32-bits of that number. Then it does NOT (~) operation on the number to toggle all bits. After toggling it prints the bits of the number.

Here is the output.

Toggle a Particular Bit

In the previous article I discussed about how to toggle a particular bit of a number in detail. Here we’ll see the program.

#include <stdio.h>

void binary(unsigned int n)
{
	unsigned int mask = 0x80000000;
    while(mask) {
	  printf("%d", (n&mask)?1:0);
	  mask = mask >> 1;
	}
}

void main()
{
    unsigned int num = 0;
	int pos = 0;
	
    printf("Enter an integer: ");
    scanf("%d", &num);

    printf("Binary represntation of the input number:\n");
    binary(num);
    
    printf("\nEnter a bit position to toggle (0-31): ");
    scanf("%d", &pos);
    
    num = num ^ (0x01 << pos);
    
    printf("\n\nAfter toggling %d-th bit of the number:\n", pos);
    binary(num);
    printf("\n");
}

Here is the output.

Toggle All but a Particular Bit

Say we want to toggle all bits of an number but the k-th bit should remain unchanged. To do that we have to first toggle the k-th bit and then toggle all bits. So the k-th would be toggled twice. That means that will remain unchanged. Other bits would be toggled once.

#include <stdio.h>

void binary(unsigned int n)
{
	unsigned int mask = 0x80000000;
    while(mask) {
	  printf("%d", (n&mask)?1:0);
	  mask = mask >> 1;
	}
}

void main()
{
    unsigned int num = 0;
	int pos = 0;
	
    printf("Enter an integer: ");
    scanf("%d", &num);

    printf("Binary represntation of the input number:\n");
    binary(num);
    
    printf("\nEnter a bit position that will remain unchanged (0-31): ");
    scanf("%d", &pos);
    
    num = ~(num ^ (0x01 << pos));
    
    printf("\n\nAfter toggling all but %d-th bit of the number:\n", pos);
    binary(num);
    printf("\n");
}

Here is the output.

In this example, all bits of the input number toggled expect bit 7 (starting from 0)

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