How to pass reference to the function

Question

I converted some VB Code to C# . Now I am stuck up at this point where I have to pass the parameters using ref keyword. The function is

CurrentZone.Radius = ModSoftUniversal.perirad(ref  (Z2 - Z1), ref ( Xval - Xinc - CurrentZone.Centerx), ref ( dXval - CurrentZone.Centerx), ref ErrorFlag);

The parameters in the function are doing some sott of calculation and to pass the values to the function , ref has to be used. Visual Studio shows the following . I need help in passing the parameters

Answer 1

You can't pass expression by reference. Add temporary variable like this:

var z = Z2 - Z1;
var x1 = Xval - Xinc - CurrentZone.Centerx;
var x2 = dXval - CurrentZone.Centerx;
CurrentZone.Radius = ModSoftUniversal.perirad(ref z, ref x1, ref x2, ref ErrorFlag);

Answer 2

Make the code like this

var z1z2Result = (Z2 - Z1);
var xValxIncres = (Xval - Xinc - CurrentZone.Centerx);
var dxValResult = (dXval - CurrentZone.Centerx);

ModSoftUniversal.perirad(ref  z1z2Result, ref xValxIncres, ref dxValResult, ref ErrorFlag);

The reason is you can't make something byreference if it isn't assigned to a variable it can reference itself to