Variables are used to store data that can be used and manipulated throughout a program. Each variable has a type that determines what kind of data it can hold, such as integers, floating-point numbers, characters, strings, and more. Below, I'll provide an overview of variables in C#, including their declaration, initialization, and examples.

Variable Declaration and Initialization

1. Declaration: This is the process of defining a variable's name and type.
2. Initialization: This is the process of assigning a value to the variable.

Basic Data Types in C#

Here are some common data types in C#:

• int: Represents a 32-bit signed integer.
• float: Represents a single-precision floating-point number.
• double: Represents a double-precision floating-point number.
• char: Represents a single 16-bit Unicode character.
• string: Represents a sequence of characters.
• bool: Represents a Boolean value (true or false).

Example Code

Here’s a simple example that demonstrates the declaration and initialization of various variable types:

csharp
1using System;
2
3class Program
4{
5    static void Main()
6    {
7        // Integer variable
8        int age = 30;
9        Console.WriteLine("Age: " + age);
10
11        // Floating-point variable
12        float height = 5.9f; // Note the 'f' suffix for float
13        Console.WriteLine("Height: " + height);
14
15        // Double variable
16        double weight = 70.5; // No suffix needed for double
17        Console.WriteLine("Weight: " + weight);
18
19        // Character variable
20        char initial = 'A';
21        Console.WriteLine("Initial: " + initial);
22
23        // String variable
24        string name = "John Doe";
25        Console.WriteLine("Name: " + name);
26
27        // Boolean variable
28        bool isStudent = false;
29        Console.WriteLine("Is Student: " + isStudent);
30    }
31}

Variable Naming Rules

When naming variables in C#, keep the following rules in mind:

• Variable names must start with a letter or an underscore (_).
• They can contain letters, digits, and underscores.
• Variable names cannot contain spaces or special characters (like @, #, $, etc.).
• Variable names are case-sensitive (e.g., myVar and MyVar are different).
• Avoid using reserved keywords (like int, class, void, etc.) as variable names.

Example of Variable Naming

csharp
1int score; // Valid
2float _temperature; // Valid
3string userName; // Valid
4bool isActive; // Valid
5
6// Invalid examples:
7// int 1stPlace; // Invalid: cannot start with a digit
8// string first name; // Invalid: cannot contain spaces
9// float @value; // Invalid: cannot use reserved keywords

Constants

In C#, you can define constants using the const keyword. Constants are variables whose values cannot be changed once they are initialized.

csharp
1const double Pi = 3.14159;
2Console.WriteLine("Value of Pi: " + Pi);

Using Variables in Operations

You can perform various operations using variables, such as arithmetic operations, string concatenation, and logical operations.

csharp
1int a = 10;
2int b = 20;
3int sum = a + b; // Arithmetic operation
4Console.WriteLine("Sum: " + sum);
5
6string firstName = "John";
7string lastName = "Doe";
8string fullName = firstName + " " + lastName; // String concatenation
9Console.WriteLine("Full Name: " + fullName);
10
11bool isAdult = age >= 18; // Logical operation
12Console.WriteLine("Is Adult: " + isAdult);