Why it prints unexpected values?

Question

#include <iostream>

using namespace std;

class calculator {
public:
    int n1, n2;

    friend void setNumbers(calculator v);
    friend void getNumbers(calculator v);
};

void setNumbers(calculator v) {
    cin >> v.n1 >> v.n2;
}

void getNumbers(calculator v) {
    cout << v.n1 << ' ' << v.n2 << '\n';
}

int main() {
    calculator calc;
    setNumbers(calc);
    getNumbers(calc);
    return 0;
}

When I call getNumbers function, it prints totally different values which I didn't input. For example when I input 3 6, it prints 0 1, while I expected 3 6. What could be wrong?

Important reading: [What's the difference between passing by reference vs. passing by value?](https://stackoverflow.com/questions/373419/whats-the-difference-between-passing-by-reference-vs-passing-by-value) — user4581301, Apr 11 '20 at 02:14
@user4581301 I tried to add the calculator &v, it gives me error. — Devonstark, Apr 11 '20 at 02:15
Why are your functions `friend`s instead of usual member functions? — walnut, Apr 11 '20 at 02:16
Perhaps you added it to one declaration of each function instead of both. It's as good a guess as any. — chris, Apr 11 '20 at 02:17

score 0 · Accepted Answer · answered Apr 11 '20 at 02:33

Passing the object without a reference won't change the values of your calculator object when you expect them to be initialized by your input values after a call to setNumbers. Instead they'll have garbage values since they are not initialized for getNumbers.

Pass the calculator objects via reference by using & as mentioned in the comments and you're good to go.

class calculator 
{
    public:
    int n1, n2;
    friend void setNumbers(calculator &v);
    friend void getNumbers(calculator &v);

};

void setNumbers(calculator &v) {
    cin >> v.n1 >> v.n2;
}

void getNumbers(calculator &v) {
    cout << v.n1 << ' ' << v.n2 << '\n';
}

Why it prints unexpected values?

1 Answers1