[c++] "&" meaning after variable type

Possible Duplicate:
What are the differences between pointer variable and reference variable in C++?
What's the meaning of * and & when applied to variable names?

Trying to understand meaning of "&" in this situation

void af(int& g)
{
    g++;
    cout<<g;
}

If you call this function and pass variable name - it will act the same like normal void(int g). I know, when you write &g that means you are passing address of variable g. But what does it means in this sample?

It means you're passing the variable by reference.

In fact, in a declaration of a type, it means reference, just like:

int x = 42;
int& y = x;

declares a reference to x, called y.

The & means that the function accepts the address (or reference) to a variable, instead of the value of the variable.

For example, note the difference between this:

void af(int& g)
{
    g++;
    cout<<g;
}

int main()
{
    int g = 123;
    cout << g;
    af(g);
    cout << g;
    return 0;
}

And this (without the &):

void af(int g)
{
    g++;
    cout<<g;
}

int main()
{
    int g = 123;
    cout << g;
    af(g);
    cout << g;
    return 0;
}