Multiple Return Values

Multiple Return Values

HolyC functions can only return a single value, like C. To return multiple values, you use output parameters — pointers that the function writes into.

Output Parameters

Pass pointers as extra arguments, and the function writes its results through them using the dereference operator *:

U0 Divide(I64 a, I64 b, I64 *quotient, I64 *remainder) {
  *quotient  = a / b;
  *remainder = a % b;
}

I64 q, r;
Divide(17, 5, &q, &r);
Print("17 / 5 = %d remainder %d\n", q, r);
// 17 / 5 = 3 remainder 2

The & operator takes the address of a variable, giving a pointer to it. The * operator on the left of an assignment dereferences the pointer and writes through it.

Another Example: Min and Max

U0 MinMax(I64 a, I64 b, I64 *mn, I64 *mx) {
  if (a < b) {
    *mn = a;
    *mx = b;
  } else {
    *mn = b;
    *mx = a;
  }
}

I64 lo, hi;
MinMax(7, 3, &lo, &hi);
Print("min=%d max=%d\n", lo, hi);
// min=3 max=7

Returning a Struct

For complex return values, you can define a class and return it by value:

class Pair {
  I64 first, second;
};

Pair MakePair(I64 a, I64 b) {
  Pair p;
  p.first  = a;
  p.second = b;
  return p;
}

Pair result = MakePair(10, 20);
Print("%d %d\n", result.first, result.second);

Your Task

Write U0 Swap(I64 *a, I64 *b) that swaps the values at two pointers.

Then declare I64 x = 3 and I64 y = 9, swap them, and print x=%d y=%d.

Expected output: x=9 y=3