GATE CSE 2020 Q58: Value of pp(3, 4) for binary exponentiation code

int tob(int b, int* arr) {
  int i;
  for (i=0; b>0; i++) {
    if (b%2) arr[i]=1;
    else     arr[i]=0;
    b = b/2;
  }
  return(i);
}

int pp(int a,int b) {
  int arr[20];
  int i, tot = 1, ex, len;
  ex = a;
  len = tob(b,arr);
  for (i=0; i<len; i++) {
    if (arr[i]==1)
      tot = tot * ex;
    ex = ex * ex;
  }
  return(tot);
}