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C++ program to clear Kth bit of a number

Program to clear the Kth bit of a number in C++: Here, we are going to use bitwise operators to clear Kth bit in the binary representation of a given number.
Submitted by Saksham Bhayana, on January 07, 2019

Here we are going to use bitwise operators to clear Kth bit in the binary representation of a given number.

Problem Statement: To write a C++ program to clear Kth bit of a number.

Constraints: 1<=n<=100

Example:

    Input:
    Enter number: 11
    Enter k: 4

    Output:
    original number before clearing: 11
    new number after clearing: 3

Problem Explanation:

Suppose the given number is 11 and the bit to be cleared is 4th bit that is 3 left to the LSB.

Now the binary representation of 11 is:

    n = 00001011
    mask = 00001000 (left shift 1, three times (4-1) as k=4)
    Bitwise complement of mask= ~mask = 11110111
    n &(~ mask) = 00000011
    Hence decimal representation of new number is 3.

This can be explained as follows:

Performing & with the ~mask clears Kth bit only as Kth bit in (~mask) is 0.

If X represents bits of n then, 0 & X is always 0. For remaining bits of original number, & with 1 gives the bit itself.

Therefore performing bitwise AND of original number with (~mask) clears Kth bit in a number.

Algorithm:

  1. Input the number and Kth bit to be cleared.
  2. Left shift 1 - (K-1) times to create a mask where only Kth bit is set.
  3. Take bitwise complement of the mask.
  4. Perform bitwise AND of original number with this mask to clear the Kth bit.
  5. Output the result after bitwise AND in decimal form.

C++ Implementation:

#include <iostream>
using namespace std;

int clearKthBit(int n,int k)
{
	// left shift 1 , (k-1) times to get a mask 
	// in which only kth bit is set
	int m=1<<(k-1); 
	// bitwise complement of mask
	m=~(m);
	// new number after clearing kth bit 
	return (n&m);   
}

//driver program to check the code

int main()
{
	int num,k;

	cout<<"Enter number: ";
	cin>>num;
	cout<<"Enter k: ";
	cin>>k;

	cout<<"original number before clearing: "<<num<<endl;

	int new_number= clearKthBit(num,k);

	cout<<"new number after clearing: "<<new_number<<endl;

	return 0;
}

Output

Enter number: 11
Enter k: 4
original number before clearing: 11
new number after clearing: 3 




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