void main() {
  mul(10, 20);
}

void mul(int a, int b) {
  int c;
  c = a * b;
  print(c);
}

o/p: 200

function with return type

void main() {
  print(mul(10, 20));
}

int mul(int a, int b) {
  int c;
  c = a * b;
  return c;
}

o/p : 200