C++ functions won't return values

Question

#include<iostream>
#include<cstdlib>
#include<string>
#include<time.h>
using namespace std;

//Functions
// player strategy
int strategy(int user1Strat, int user2Strat);
// player total score per round
int currentScore();
// Display game result
void printResults();

int main()
{
    int total_player1 = 0; // player 1 current score
    int total_player2 = 0; // player 2 current score
    int player1_strat= 0;  //player 1 strategy for each turn
    int player2_strat = 0; // player 2 strategy for each turn

    // seed the random number generator.
    srand(static_cast<int> (time(NULL)));

    // get strategy for each player using functions <strategy>

    strategy(player1_strat, player2_strat);

    cout << player1_strat << endl << player2_strat << endl;

    system("pause");
    return 0;
}

int strategy(int user1Strat, int user2Strat)
{
    int x,
        y;

    cout << "Enter player1's roll until strategy: ";
    cin >> user1Strat;
    cout << "Enter player2's roll until strategy: ";
    cin >> user2Strat;
    x = user1Strat;
    y = user2Strat;

    return x, y;
}

While calling for function strategy in the function main it will execute how it should, but once I ask to return the value it will just return

Enter player1's roll until strategy: 10
Enter player2's roll until strategy: 5

0
0

press any key to contiue...

Does anyone know why this is happening or what is causing it, was my error in the strategy function? Or upon calling it?

That's not how you return multiple values in C++ from a function. Look up "returning by reference". — Bob, May 02 '16 at 05:13
Your understanding of returning values from functions is flawed. Please read a textbook on the subject. — R Sahu, May 02 '16 at 05:13
Also you don't take any return value from the function anyway. X and y don't magically appear on some random variables you would like. A basics tutorial/book will help you here. — Sami Kuhmonen, May 02 '16 at 05:20
The `strategy` function should return a `std::pair`, not a single `int`. — David Schwartz, May 02 '16 at 06:06
Possible duplicate of [Returning two variables in a C++ function](http://stackoverflow.com/questions/15365860/returning-two-variables-in-a-c-function) — dandan78, May 02 '16 at 06:08

Rahn · Accepted Answer · 2016-05-02T05:43:54.510

strategy(player1_strat, player2_strat); in your main() do nothing after receiving inputs so you won't see any change on player1_strat and player2_strat.

If you want to modify player1_strat and player2_strat in strategy, you could do that by referencing:

void strategy(int& user1Strat, int& user2Strat)
{
    cout << "Enter player1's roll until strategy: ";
    cin >> user1Strat;
    cout << "Enter player2's roll until strategy: ";
    cin >> user2Strat;
}

or you could return "multiple value" by using std::pair:

//#include <utility>
std::pair<int, int> strategy(int user1Strat, int user2Strat)
{
    int x, y;

    cout << "Enter player1's roll until strategy: ";
    cin >> user1Strat;
    cout << "Enter player2's roll until strategy: ";
    cin >> user2Strat;
    x = user1Strat;
    y = user2Strat;

    return std::make_pair(x, y);
}

//main()
std::pair<int, int> result = strategy(player1_strat, player2_strat);

x = result.first;
y = result.second;

Alexander Büse · Answer 2 · 2016-05-02T06:25:29.310

0

You can only return a single object from a function. return x, y; does not return x and y but only y. If you want to update multiple variables, give them to the function as references and change their value inside the function.

Edit:

As mentioned by @Keith Thompson in the comments, the comma actually is an operator in this statement. It evaluates x (not much to do there), discards the result and then evaluates and returns the second argument y.

edited May 02 '16 at 06:25

answered May 02 '16 at 05:13

Alexander Büse

564
7
15

1

*`return x, y;` is not allowed.* It is syntactically valid. It doesn't do what the OP is expecting. – R Sahu May 02 '16 at 05:15
@RSahu You are right that was not precise. I'll edit my answer. – Alexander Büse May 02 '16 at 05:16
eh, would "return x, y" return x and treat "y" as another expression by itself? – Einheri May 02 '16 at 06:10
1

You should mention the comma operator. – Keith Thompson May 02 '16 at 06:21
@KeithThompson True. Updated my answer. Thanks for your comment. – Alexander Büse May 02 '16 at 06:26
1

@user3109672: `return x, y;` is equivalent to `return(x, y);` — that is, `x` is evaluated and the result discarded, then `y` is evaluated and the value of `y` is returned. Normally, the evaluation of `x` will have some side-effect; here is doesn't, and a compiler would probably warn about that (at least if warnings and/or optimization is enabled). – Jonathan Leffler May 02 '16 at 06:41

C++ functions won't return values

2 Answers2