How to turn off a particular bit in a number?

Given a number n and a value k, turn of the k’th bit in n.

Examples:

Input:  n = 15, k = 1
Output: 14

Input:  n = 15, k = 2
Output: 13

Input:  n = 15, k = 3
Output: 11

Input:  n = 15, k = 4
Output: 7

Input:  n = 15, k >= 5
Output: 15 

The idea is to use bitwise <<, & and ~ operators. Using expression "~(1 << (k - 1))“, we get a number which has all bits set, except the k’th bit. If we do bitwise & of this expression with n, we get a number which has all bits same as n except the k’th bit which is 0.

Following is C++ implementation of this.

#include <iostream> using namespace std;   // Returns a number that has all bits same as n // except the k'th bit which is made 0 int turnOffK(int n, int k) {     // k must be greater than 0     if (k <= 0) return n;       // Do & of n with a number with all set bits except     // the k'th bit     return (n & ~(1 << (k - 1))); }   // Driver program to test above function int main() {     int n = 15;     int k = 4;     cout << turnOffK(n, k);     return 0; } Output: 7