#include <iostream>

/***************************************************
 * Resetting a variable and returning its original
 * value
 *
 * Write a function that performs two operations:
 *
 *   1. Reset the argument to 0.
 *   2. Return the original value of the argument.
 *
 * For example, if
 *
 *     m == 42,
 *
 * then after
 *
 *     int n{ reset( m ) };
 *
 * we should have
 *
 *     m == 0
 *     n == 42.
 *
 * The parameter must be passed by reference because
 * the function must modify the variable supplied by
 * the calling function.
 *
 * The return value allows the function to also give
 * the original value back to the calling function.
 ***************************************************/

// Function declarations
int main();
int reset( int &a );

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

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

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

    std::cout << reset( m ) << std::endl;
    std::cout << reset( n ) << std::endl;

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

    return 0;
}

/***************************************************
 * reset
 *
 * Reset the argument to 0 and return its original
 * value.
 ***************************************************/
int reset( int &a ) {
    return 0;
}






































// Hint:
//
// You must do three things, in the correct order:
//
//   1. Store the original value of a.
//   2. Assign 0 to a.
//   3. Return the stored original value.
//
// Why must you save the original value before
// assigning 0 to a?




































// Solution:

/*
int reset( int &a ) {
    int const original{ a };
    a = 0;

    return original;
}
*/


/***************************************************
 * Notice that original is declared const.
 *
 * Once we have copied the original value of a into
 * original, there is no reason for original to
 * change.
 *
 * The parameter a cannot be const because the
 * purpose of the function is to modify the variable
 * to which a refers.
 *
 * Thus, this function demonstrates two different
 * ways information can pass out of a function:
 *
 *   - through a reference parameter; and
 *   - through the return value.
 ***************************************************/