Help with templates in C++

[reptile]

Why doesn't this code work???

template<class t>
t sum( t a, t b )
{
	return a + b;
}

template<class t>
class c_x {
public:
	t a, b, c;

	void sum()
	{
		c = sum( a, b );
	}
};

void main()
{
	c_x<int> x;
	x.a = 10;
	x.b = 20;
	x.sum();
}

Error
C2660: 'c_x<t>::sum' : function does not take 2 arguments
with
[
t=int
]

[Mick]

template<class t>
t sum( t a, t b )
{
	return a + b;
}

	void sum()
	{
		c = sum( a, b );
	}

in case you don't get it, what does:

sum(a,b) resolve to in class c_x...