使用函数返回多个值 C++

Question

I have to create a function that will do all the processing (the billsHundred to coinLoonie calculation), but input and output to console will still be done in int main. How should I go about this. I am really having an issue with producing multiple outputs from the function int cash() so i left that blank in order to see what you guys would suggest.

#include <iostream>
#include <cmath> 
#include <iomanip>
using namespace std;

int cash();

int main()
{
    int dollarAmount;

    for (int i = 1; i <= 3; i++)
    {
        cout << "Enter the total dollar amount: $";
        cin >> dollarAmount;

        while (cin.fail())
        {
            cout << "\nThat entry is not valid. Please try again: ";
            cin.clear();
            cin.ignore(1000, '\n');
            cin.clear();
            cin >> dollarAmount;
        }

        int billsHundred = dollarAmount / 100;
        int billsFifty = (dollarAmount - (100 * billsHundred)) / 50;
        int billsTwenty = (dollarAmount - (100 * billsHundred) - (50 *  billsFifty)) / 20;
        int billsTen = (dollarAmount - (100 * billsHundred) - (50 * billsFifty) - (20 * billsTwenty)) / 10;
        int billsFive = (dollarAmount - (100 * billsHundred) - (50 * billsFifty) - (20 * billsTwenty) - (10 * billsTen)) / 5;
        int coinToonie = (dollarAmount - (100 * billsHundred) - (50 * billsFifty) - (20 * billsTwenty) - (10 * billsTen) - (5 * billsFive)) / 2;
        int coinLoonie = (dollarAmount - (100 * billsHundred) - (50 * billsFifty) - (20 * billsTwenty) - (10 * billsTen) - (5 * billsFive) - (2 * coinToonie)) / 1;

        cout << "\nNumber of 100$ bills = " << billsHundred;
        cout << "\nNumber of 50$ bills = " << billsFifty;       
        cout << "\nNumber of 20$ bills = " << billsTwenty;      
        cout << "\nNumber of 10$ bills = " << billsTen;     
        cout << "\nNumber of 5$ bills = " << billsFive;     
        cout << "\nNumber of Toonies = " << coinToonie;     
        cout << "\nNumber of Loonies = " << coinLoonie << endl << endl;
    }
    cout << endl;
    return 0;
}

int cash()
{


}

Answer 1

There are basically two ways to return multiple values. You either return a struct or class as the return value, or you pass in reference values or pointers and the function sets the referred to/pointed to value.

So if you have to break an amount into 10s and 1s:

struct Change {
    int Tens;
    int Ones;
};

Change cash(int amount) {
    Change result;
    result.Tens = amount / 10;
    result.Ones = amount % 10;
    return result;
}

Change broken = cash(15);
// Refer to broken.Tens and broken.Ones.

Alternatively:

void cash(int amount, int& tens, int& ones) {
    tens = amount/10;
    ones = amount%10;
}

int tens;
int ones;
cash(15, tens, ones);

In your application, I would use the struct - a function with seven output arguments has too many arguments.

Answer 2

To answer your question, you can't really return multiple values from a function in C++. Instead, you could return a struct or some other object that contains or references multiple things. For example:

#include <iostream>

struct Foo {
    int x;
    int y;
};

Foo doSomething() {
    Foo f;
    f.x = 10;
    f.y = 20;
    return f;
}

int main()
{
    Foo f = doSomething();
    std::cout <<  f.x << std::endl;
    std::cout << f.y << std::endl;
}

Based on the rest of the code above, though, I think might do better calling multiple functions ( getBillsHundred() , etc.), or a single function with different parameters ( getBillsBySize() ) for each of the different sizes. Each of those functions would just return one value.

Answer 3

You can consider using a map.

std::map<string, int> cash(int dollarAmount) {
    std::map<string, int> ret;
    ret['hundred'] = dollarAmount / 100;
    // stuff similar
    return ret;
}