C/C++ Program to Count set bits in an integer

Last Updated : 14 May, 2025

Write an efficient program to count number of 1s in binary representation of an integer.

Examples :

Input : n = 6
Output : 2
Binary representation of 6 is 110 and has 2 set bits

Input : n = 13
Output : 3
Binary representation of 11 is 1101 and has 3 set bits

1. Simple Method

Loop through all bits in an integer, check if a bit is set and if it is then increment the set bit count. See below program.

#include <stdio.h>

/* Function to get no of set bits in binary
   representation of positive integer n */
unsigned int countSetBits(unsigned int n)
{
    unsigned int count = 0;
    while (n) {
        count += n & 1;
        n >>= 1;
    }
    return count;
}

/* Program to test function countSetBits */
int main()
{
    int i = 9;
    printf("%d", countSetBits(i));
    return 0;
}

 
#include <stdio.h>
​/* Function to get no of set bits in binary   representation of positive integer n */unsigned int countSetBits(unsigned int n){    unsigned int count = 0;    while (n) {        count += n & 1;        n >>= 1;    }    return count;}​/* Program to test function countSetBits */int main(){    int i = 9;    printf("%d", countSetBits(i));    return 0;}

Output

Recursive Approach :

// Cpp implementation of recursive
// approach to find the number
// of set bits in binary representation
// of positive integer n
#include <bits/stdc++.h>
using namespace std;

// recursive function to count set bits
int countSetBits(int n)
{
    // base case
    if (n == 0)
        return 0;

    else

        // if last bit set add 1 else add 0
        return (n & 1) + countSetBits(n >> 1);
}

// driver code
int main()
{
    // get value from user
    int n = 9;

    // function calling
    cout << countSetBits(n);

    return 0;
}

// This code is contributed by Raj.

 
// Cpp implementation of recursive
// approach to find the number// of set bits in binary representation// of positive integer n#include <bits/stdc++.h>using namespace std;​// recursive function to count set bitsint countSetBits(int n){    // base case    if (n == 0)        return 0;​    else​        // if last bit set add 1 else add 0        return (n & 1) + countSetBits(n >> 1);}​// driver codeint main(){    // get value from user    int n = 9;​    // function calling    cout << countSetBits(n);​    return 0;}​// This code is contributed by Raj.