Initial commit

vscode/Chapter02/Variables/Program.cs

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+using System.Xml;
+
+object height = 1.88; // storing a double in an object 
+object name = "Amir"; // storing a string in an object
+Console.WriteLine($"{name} is {height} metres tall.");
+
+//int length1 = name.Length; // gives compile error!
+int length2 = ((string)name).Length; // tell compiler it is a string
+Console.WriteLine($"{name} has {length2} characters.");
+
+// storing a string in a dynamic object
+// string has a Length property
+dynamic something = "Ahmed";
+
+// int does not have a Length property
+something = 12;
+// an array of any type has a Length property
+something = new[] { 3, 5, 7 };
+
+// this compiles but would throw an exception at run-time
+// if you later store a data type that does not have a
+// property named Length
+Console.WriteLine($"Length is {something.Length}");
+
+var population = 66_000_000; // 66 million in UK
+var weight = 1.88; // in kilograms
+var price = 4.99M; // in pounds sterling
+var fruit = "Apples"; // strings use double-quotes
+var letter = 'Z'; // chars use single-quotes
+var happy = true; // Booleans have value of true or false
+
+// good use of var because it avoids the repeated type
+// as shown in the more verbose second statement
+var xml1 = new XmlDocument(); // C# 3 and later
+XmlDocument xml2 = new XmlDocument(); // all C# versions
+
+// bad use of var because we cannot tell the type, so we
+// should use a specific type declaration as shown in
+// the second statement
+var file1 = File.CreateText("something1.txt");
+StreamWriter file2 = File.CreateText("something2.txt");
+
+Console.WriteLine($"default(int) = {default(int)}");
+Console.WriteLine($"default(bool) = {default(bool)}");
+Console.WriteLine($"default(DateTime) = {default(DateTime)}");
+Console.WriteLine($"default(string) = {default(string)}");
+
+int number = 13;
+Console.WriteLine($"number has been set to: {number}");
+number = default;
+Console.WriteLine($"number has been reset to its default: {number}");

vscode/Chapter02/Variables/Variables.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>