Given a Number - N, count the number of set bits in N.

setbits.cpp

// Refer checkith() function here: https://gist.github.com/Ch-sriram/fef3d0a6274d20f6705495b7cf5b22e4
bool checkith (long long N, int i) {
  return N & ((long long) 1 << i);
}

int countSetBits (long long N) {
  int count = 0;
  for (int i = 0; i < 64; ++i)
    if (checkith(N, i))
      ++count;
  return count;
}