Toggle all the bits of a number except k-th bit.

3

Given a positive (or unsigned) integer n, write a function to toggle all the bits except k-th bit. Here value of k starts from 0 (zero) and from right.

Examples:

Input : n = 4294967295, k = 0
Output : 1
The number 4294967295 in 32 bits has all bits
set.  When we toggle all bits except last bit,
we get 1.

Input  :  n = 1, k = 1
Output : 4294967292
4294967262 has all bits toggled except second
bit from right.
  1. Toggle bit at k-th position. We do it by finding a number with only k-th bit set (using 1 << k), then doing bitwise XOR of this number n.
  2. Toggle all bits of number obtained above using ~ (Bitwise negation)
// C program to toggle all bits except kth bit
#include<stdio.h>

// Returns a number with all bit toggled in n
// except k-th bit
unsigned int toggleAllExceptK(unsigned int n,
                            unsigned int k)
{
   /* 1) Toggle k-th bit by doing n ^ (1 << k)
      2) Toggle all bits of the modified number */
    return ~(n ^ (1 << k));
}

// Driver code
int main()
{
    unsigned int n = 4294967295;
    unsigned int k = 0;
    printf("%u", toggleAllExceptK( n, k));
    return 0;
}

Output:

1

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