Small Steps V — Making Your Own Types

Naming the original instead of copying

Name the original instead of copying it.

What you will learn

A reference is another name for an existing object. An int& parameter refers to the original integer passed in.

Try it

void add_one(int x)
{
    x = x + 1;
    print("Inside: ", x);
}

void small_main()
{
    int n = 10;

    add_one(n);

    print("Outside: ", n);
}

First run the example: it prints Inside: 11 and Outside: 10. Change add_one(int x) to add_one(int& x) and run again. Now both are 11.

Initially x was a copy; after adding &, it is another name for n. Use this when you intend to change the original.

Exercise

Create swap(int& a, int& b) to exchange the original values of two ints.

void swap(int& a, int& b)
{
    // swap the original values.
}

void small_main()
{
    int x = 3;
    int y = 7;

    swap(x, y);

    print(x, ", ", y);
}

Hint

Save a temporarily in temp, then assign a=b and b=temp.

void swap(int& a, int& b)
{
    int temp = a;
    a = b;
    b = temp;
}

void small_main()
{
    int x = 3;
    int y = 7;

    swap(x, y);

    print(x, ", ", y);
}