#include <iostream>

/***************************************************
 * Swapping two local variables by reference
 *
 * Write a function that swaps the values of two
 * variables passed as arguments.
 *
 * Normally, function parameters are passed by value.
 * This means that the parameters are local copies
 * of the arguments supplied by the calling function.
 *
 * For example, if we declared
 *
 *     void swap( int a, int b );
 *
 * then changing a and b inside swap() would not
 * change the original variables.
 *
 * Instead, we will pass the parameters by reference:
 *
 *     void swap( int &a, int &b );
 *
 * A reference parameter refers to the original
 * variable supplied as the argument. Consequently,
 * assigning a new value to a or b changes the
 * corresponding variable in the calling function.
 ***************************************************/

// Function declarations
int main();
void swap( int &a, int &b );

// Function definitions
int main() {
    int m{ 42 };
    int n{ 91 };

    std::cout << "m == " << m
              << " and n == " << n
              << std::endl;

    std::cout << "Swapping m and n..."
              << std::endl;

    swap( m, n );

    std::cout << "m == " << m
              << " and n == " << n
              << std::endl;

    return 0;
}

/***************************************************
 * swap
 *
 * Swap the values of the two arguments.
 *
 * Because a and b are reference parameters, changes
 * made to a and b also change the variables passed
 * as arguments.
 ***************************************************/
void swap( int &a, int &b ) {
    return;
}






































// Hint:
//
// Because a and b are references to the original
// variables, you can treat them just as you would
// treat two local variables that you wanted to swap.
//
// You will need a temporary variable:
//
//     temporary = a
//     a = b
//     b = temporary
//
// Be careful to save the original value of a before
// overwriting it.




































// Solution:

/*
void swap( int &a, int &b ) {
    int temporary{ a };
    a = b;
    b = temporary;
}
*/


/***************************************************
 * Afterthought
 *
 * C++ already provides a function for swapping two
 * values. After including <utility>, we could write
 *
 *     std::swap( m, n );
 *
 * The purpose of writing our own swap() function
 * here is to demonstrate reference parameters and
 * how a function can modify variables belonging to
 * the calling function.
 ***************************************************/