When pass a variable to a function, why the function only gets a duplicate of the variable?

Question

When pass a variable to a function, why the function only gets a copy/duplicate of the variable?

int n=1;

void foo(int i)
{
    i++;
}

As

Answer 1

Depending on what you're trying to do, you can do this:

int n = 1;

n = foo(n);

Just make sure foo(int i) returns i after modifying it.