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

Here we will see how we can check number of set bits in an integer number. The set bits are 1’s in the binary representation of a number. For an example the number 13 has three set bits 1101. So the count will be 3.

To solve this problem, we will shift the number to the right, and if the LSb is 1, then increase count. Until the number becomes 0, it will run.

Algorithm

countSetBit()

begin
   count := 0
   while count is not 0, do
      if LSb of n is set, then
         count := count + 1
      end if
         n := n after shifting 1 bit to right
   done
   return count
end

Example

 Live Demo

#include<iostream>
using namespace std;
int count_set_bit(int n) {
   int count = 0;
   while(n != 0) {
      if(n & 1 == 1) {
         count++;
      }
      n = n >> 1; //right shift 1 bit
   }
   return count;
}
int main() {
   int n;
   cout << "Enter a number: ";
   cin >> n;
   cout << "Number of set bits: " << count_set_bit(n);
}

Output

Enter a number: 29
Number of set bits: 4

This program will run in C and generates output, but when we want to compile in C++, it will return an error during compile time. It will say there are too many arguments are passed.