You could add a vector pointer as an argument/ parameter, (and/) or use a static vector:

Code:
void foo(VECTOR* v, var x, var y, var z)
{
	v->x = x;
	v->y = y*2;
	v->z = z*3;
}

VECTOR* foo(VECTOR* v, var x, var y, var z)
{
	v->x = x;
	v->y = y*2;
	v->z = z*3;

	return v; // now you can use the function as an argument where VECTOR* is expected
}

// same function but accepts NULL as "v" as well
VECTOR* foo(VECTOR* v, var x, var y, var z)
{
	static VECTOR _v;
	if(!v) v = &_v;
	v->x = x;
	v->y = y*2;
	v->z = z*3;

	return v;
}

VECTOR* foo(var x, var y, var z)
{
	static VECTOR _v;
	_v.x = x;
	_v.y = y*2;
	_v.z = z*3;

	return &_v;
}

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