A very easy way to invoke return and non return value subroutines. is using Func and Action respectively. (see also https://msdn.microsoft.com/en-us/library/018hxwa8(v=vs.110).aspx)
Try this this example
using System;
public class Program
{
private Func FunctionPTR = null;
private Func FunctionPTR1 = null;
private Action