Calculate the Number of "1" in the Binary Form of a Positive Integer

Problem: Given a positive integer, count the number of "1" in its binary form. For example, the binary form of "7" is "111", so the number of "1" is 3.

Solution: There is an elegant solution with a complexity of O(k) where k is the number of "1". The code is as follow:

int cout_numof1(int n)
{
 
   int cnt = 0;

   while(n)
   {
      n = n & (n-1);
      cnt++;
   }
  
   return cnt;
}