How to turn off a particular bit in a number in C++ ?

In this tutorial, we will see how to turn off a particular bit in a number in C++.

Any number can be represented in its binary form which contains 0s and 1s. And we want to convert a 1 into 0(turn off) at any given position.

Let’s assume a number :

int num = 5;  // 5 is 101 in binary 
int position = 0; // turn off 1 at 0th position

// final answer should be 4 as 101 will become 100 which is 4 in decimal.

Let’s take another example:

int num1 = 7;  // 7 is 111 in bianry
int position = 1; 

// final answer should be 5 as 111 will become 101 which is 5 in decimal.

Turning off a bit in a number in C++

Here we will use the bitwise operators on the given number. The bitwise operators used are :

• << (left shift) : num << x  this statement shifts the bits of the number by x places.

// 9 is 00001001
9 << 2  // left shifting by 2 places

// 00100100 
result is 32.

• &(bitwise and): num & x this statement does a bitwise and is similar to the logical operator && but on bits.

// 11011 & 01100 

// result is 01000

• ~(compliment): ~num gives the compliment of num.

// ~1100110 is 0011001

Now the idea is to left shift 1 to the given position and then take its complement. This will leave us with a number with 0 at the position’s bit and the rest of the bits as 1. Then take bitwise and (&) of this with the given number. The & operator will turn off the position’s bit as it is 0.

The code using the above operators is given below:

#include <bits/stdc++.h>
using namespace std;

int main() {
    
    int num = 5; // 5 is 101
    int position = 0;
    
     // result should be 100 which is 4 in decimal
     
     cout<<(num & ~(1<<position)) ;
  
  return 0;
}

Output:

4