sample code

MySolution/ConsoleApp/Samples/CalculateSample.cs

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+using System;
+
+namespace Samples
+{
+    class CalculateSample
+    {
+        private delegate int Calculate(int x, int y);
+
+        public static int Add(int x, int y)
+        {
+            return x + y;
+        }
+
+        public static int Subtract(int x, int y)
+        {
+            return x - y;
+        }
+
+        public static void Sample()
+        {
+            Calculate calc1 = Add;
+            Calculate calc2 = Subtract;
+
+            Console.WriteLine(calc1(10, 5));
+            Console.WriteLine(calc2(10, 5));
+        } 
+    }
+}

MySolution/ConsoleApp/Samples/EventSample.cs

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+using System;
+
+namespace Samples
+{
+    public delegate void CustomEventHandler(object sender, EventArgs e);
+
+    class EventSample
+    {
+        public static void Sample()
+        {
+            Button button = new Button();
+            button.Click += new CustomEventHandler(Button_Click);
+
+            button.OnClick();
+        }
+
+        private static void Button_Click(object sender, EventArgs e)
+        {
+            System.Console.WriteLine("Button clicked!");
+        }
+    }
+    
+    class Button
+    {
+        public event CustomEventHandler Click;
+
+        public void OnClick()
+        {
+            if (Click != null)
+                Click(this, EventArgs.Empty);
+        }
+    }
+}

MySolution/ConsoleApp/Samples/MessagePrinterSample.cs

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+using System;
+using System.Diagnostics;
+using System.Threading.Tasks;
+
+namespace Samples
+{
+    class MessagePrinterSample
+    {
+        private delegate Task MessagePrinter(string message);
+
+        private static async Task PrintMessageAsync(string message)
+        {
+            await Task.Delay(1000);
+            Console.WriteLine(message);
+        }
+
+        public static void Sample()
+        {
+            MessagePrinter printer = PrintMessageAsync;
+            Console.WriteLine("Start...");
+            
+            printer("This is first message");
+            printer("This is second message");
+            printer("This is third message");
+            
+            Console.WriteLine("Finish...");
+        }
+    }
+}

MySolution/ConsoleApp/Samples/StringLength.cs

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+using System;
+
+namespace Samples
+{
+    class StringLength
+    {
+        public static void Sample()
+        {
+            string[] words = new string[]
+            {
+                "Apple",
+                "Banana",
+                "Cherry",
+                "Pear",
+            };
+
+            CalculateStringLength(words, PrintStingLength);
+        }
+
+        private static void CalculateStringLength(string[] words, Action<int[]> callback)
+        {
+            int[] lengths = new int[words.Length];
+            for (int i = 0; i < words.Length; i++)
+            {
+                lengths[i] = words[i].Length;
+            }
+
+            if (callback != null)
+                callback(lengths);
+        }
+
+        private static void PrintStingLength(int[] lengths)
+        {
+            foreach (int length in lengths)
+            {
+                Console.WriteLine(length);
+            }
+        }
+    }
+}