C++ Swapping an array of integers passed through an int& parameter

Question

Hi,

I need to swap a couple of integers in the format int i[2] using a void swap(int& x) function. As you see the function takes an argument of type int&. Here is non-working version of the function:

int i[2] = {3, 7};

void swap (int& x)
{
    int temp;
    temp = x[1];
    x[1] = x[0];
    x[0] = temp;
}

int main()
{
    cout << i[0] << ", " << i[1] << "\n"; // return the original: (3, 7)
    swap(i);
    cout << i[0] << ", " << i[1] << "\n"; // return i swapped: (7, 3)
}

How should I do this?

Edit: The answer CANNOT use anything else for the function parameter. It MUST use a int& parameter. This is a problem from Bjarne Stroustrup's book: "The C++ programming language", third edition. It is problem #4 from chapter 5. The problem first asks to write a function taking a int* as parameter, than to modify it to accept a int& as parameter.

Answer 1

A reference isn't a pointer. I'd recommend changing the function signature if you can, but if you're stuck with it, you could do something like:

int *xx = &x;
int temp = xx[1];
xx[1] = xx[0];
xx[0] = temp;

That said, you should probably just use std::swap instead.

Answer 2

Looking at my copy, the exercise doesn't say how swap() should look like. It just says that it "swaps (exchanges the value of) two integers" and should take a) int* b) int& as the argument type.

As you tagged the question learning, the real question becomes:
Why does your swap() only take one argument?

Answer 3

All right, thanks to @gf's suggestions, I found a solution :) Many thanks! Please tell me if you see anything not very C++ish in there.

// Swap integers

#include<iostream>

using namespace std;

int i = 3;
int j = 7;

void swap (int& x, int& y)
{
    int temp = x;
    x = y;
    y = temp;
}

int main()
{
    cout << i << ", " << j << "\n"; // return the original: (3, 7)
    swap(i, j);
    cout << i << ", " << j << "\n"; // return i swapped: (7, 3)
}