Default Values for Parameters

Question

#include <iostream>
using namespace std;

int sum(int a, int b=42) {
int result = a + b;
return (result);
}

int main() {
int x = 24;
int y = 36;

//calling the function with both parameters
int result = sum(x, y);
cout << result << endl;

//calling the function without b
result = sum(x);
cout << result << endl;

return 0;
}

For the 1st part we get 60, for the 2nd we get 66.
In the 2nd part, 1st value was taken as input using,
result = sum(x);
and the 2nd value was default.
What if I want to set default value for the 1st parameter and input the 2nd value?
How should I input the 2nd value?

Answer 1

Default values must ALWAYS be the last parameters, but you can input them in order and then swap them around for the function.