Binary Calculation.

int[]bi = new int[1000];
  int n = 20;
  int i = 0;
  while (n!=0) {
    bi[i]=n%2;
    n=n/2;
    if (n!=0) {
      i++;
    }
  }
  while (i>=0) {
    print(bi[i]);
    i--;
  }

Output
10100