/* C++ supports pass-by-reference for parameter passing during function calls.
 * This is sort of an automatic pass-by-value-with-pointers.
 * In the function signature, you indicate that a parameter is pass-by-reference using the &.
 * When calling the function, you just provide the name of the variable.
 * C++ automatically passes its address instead of its value (note the implication that this means the argument has to have an address and can't just be a literal value)
 * Then the function uses to the parameter without having to do any dereferencing
 * Here, we demonstrate with a swap function.
 * The swap functions's parameters a and b actually have their values stored in the stack frame for the main function.
 */

#include <iostream>
using namespace std;

int c_thing( int a, int b ) {
    printf( "Hi\n" );
}

// C++ has pass-by-reference
int swap (int &a, int &b) {
	int tmp = a; // put the value of a into tmp
	a = b; 
	b = tmp;
	printf( "in swap, a is at %p\n", &a );
	printf( "in swap, b is at %p\n", &b );
	printf( "in swap, tmp is at %p\n", &tmp );
	
	return 0;
}

int main () {
	int a = 3, b = 5;
	printf("in main, a is at %p\n", &a );
	printf("in main, b is at %p\n", &b );
	cout << "Before swap a = " << a << ", b = " << b << "\n";
	swap(a, b); // pass it the variables.
	cout << "After swap a = " << a << ", b = " << b << "\n";
    
    // if we use pass-by-reference, we need to provide
    // a variable as input
    // If we use pass-by-value, we can use an expression or a literal
    // value.
    c_thing( 3+5, 2 );
    //swap( 3+5, 2 ); // illegal
    
    return 0;
}