public static int c(int n, int k) {
// ---------------------------------------------------
// Computes the number of groups of k out of n things.
// Precondition: n and k are nonnegative integers.
// Postcondition: Returns c(n, k).
// ---------------------------------------------------
  if ( (k == 0) || (k == n) ) {
     return 1;
  } 
  else if (k > n) {
     return 0;
  } 
  else {
     return c(n-1, k-1) + c(n-1, k);
  }  // end if
}  // end c