Lambda Expression error when trying to call it

Question

I want use a Lambda Expression but get an error which occurs on the line commented below, when I try to call it.

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 namespace ConsoleAppTestDelegate2
 {
 public delegate string MyDelegate (int a);
 public class ClassRunDelegate
 {
 public void RunDelegate(MyDelegate a, int b)
 {
 Console.WriteLine(a(b));
 }
 }
 public class MyHelp
 {
 public string test(int a)
 {
 a++;
 return a.ToString();
 }
 }
 class Program
 {
 static void Main(string[] args)
 {
 MyHelp fhelp = new MyHelp();
 //
 MyDelegate fdelegate = new MyDelegate(fhelp.test);
 ClassRunDelegate cc = new ClassRunDelegate();
 cc.RunDelegate(fdelegate, 10); 
 ///
 cc.RunDelegate((a, b) => { Console.WriteLine("test"); });// get error this line
 Console.ReadLine();
 }
 }
 }

• George Duckett: What does the error say?
• Justin: That line isn't even valid. I don't know what you are trying to do.

Answer 1

From your code, MyDelegate should return string, but Console.WriteLine("test") does not return anything, so that does not compile:

 cc.RunDelegate((a) => { Console.WriteLine("test"); }, b);

You should either return something after Console.WriteLine or use another type of delegate, with no return value.