Add Lesson 1 Task 3

Lesson_1/Task_3/Program.cs

@@ -0,0 +1,42 @@
+/*
+* Lesson 1 Task 3: get a list of ten numbers and duplicate a number entered by user
+* Author: Stanislav Mykhailenko
+* License: Unlicense
+*/
+
+int duplicate;
+List<int> numbers = new List<int>();
+string? userInput;
+
+for (int i = 0; i < 10; i++)
+{
+	int newNumber;
+
+	do
+	{
+		Console.Write(string.Format("Enter number {0}: ", i + 1));
+		userInput = Console.ReadLine();
+	} while (!int.TryParse(userInput, out newNumber));
+
+	numbers.Add(newNumber);
+}
+
+do
+{
+	Console.Write("Enter a number to duplicate: ");
+	userInput = Console.ReadLine();
+} while (!int.TryParse(userInput, out duplicate));
+
+for (int i = 0; i < numbers.Count; i++) {
+	if (numbers[i] == duplicate)
+	{
+		numbers.Insert(i, duplicate);
+		i++;
+	}
+}
+
+Console.WriteLine(
+	string.Join(", ",
+		numbers.Select(number => number.ToString())
+	)
+);

Lesson_1/Task_3/Task_3.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>