Another noob question for you all . . .

I have functions written in C++ that I want to call from C#.  I need to
be able to pass a reference to a value type (like an int) so that the
function can change the value - just like passing a pointer to an int
in good old unmanaged C.

Here is the function in C++ (member of testclass) - this compiles to a
DLL without error in C++:

int test_function(int arg1, int^ arg2)
{
    int result;

    // arg1 is a VALUE type passed IN to the function. The
    // function can use the value but not change it.

    // arg2 is a REFERENCE to a value type, so the function
    // should be able to use the value and change the value.

    result = arg1 + *arg2;
    *arg2 = 1234;

    return( result );
}

I use the DLL from C# so I can call the function.
Here is what I am doing in C# (doesn't compile):

           int status, val1, val2;

           val1 = 11;
           val2 = 12;
           status = testclass.test_function(val1, ref val2);   //
Chokes on "ref arg2"

The error says - Argument '2': cannot convert from 'ref int' to
'System.ValueType'.

I'm sure I'm doing something fundamentally wrong here.  Can someone
here set me straight?

Thanks.