#include <iostream>
#include <cstdlib>
using namespace std;

void addTen(int& n);

int main()
{
    int x {0};

    cout << "Enter a number: ";
    cin >> x;

    if (!cin) {
        cerr << "Sorry, that wasn't a number.\n";
        return EXIT_FAILURE;
    }

    //This can change the value of x because n is a reference.
    addTen(x);

    cout << "After adding 10, your number is " << x << ".\n";

    return EXIT_SUCCESS;
}

void addTen(int& n)
{
    //n is a reference to x in main
    n = n + 10;
}