C# is a strongly typed language, meaning each variable must be explicitly declared with a type. Variables store data in memory, and the type determines what kind of data the variable can hold.

---

1. Declaring Variables

To declare a variable, specify the data type, followed by the variable name:

int number;   // Declaration
number = 10;  // Initialization

You can also declare and initialize a variable in one step:

int number = 10;

---

2. Variable Types in C#

Primitive Data Types

Data Type	Description	Example Values
int	Integer (whole numbers)	-2147483648 to 2147483647
float	Floating-point (decimal numbers)	3.14F, -5.67F
double	Double-precision floating-point	3.14159, -0.01
decimal	High precision for monetary calculations	3.14M, -12345.67M
char	Single character	'A', '9'
string	Sequence of characters	"Hello, World!"
bool	Boolean (true or false)	true, false
byte	8-bit unsigned integer	0 to 255
sbyte	8-bit signed integer	-128 to 127
short	16-bit signed integer	-32,768 to 32,767
ushort	16-bit unsigned integer	0 to 65,535
long	64-bit signed integer	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong	64-bit unsigned integer	0 to 18,446,744,073,709,551,615

---

Example of Primitive Data Types

int age = 30;
float price = 19.99F;
double pi = 3.14159;
char initial = 'A';
string name = "Alice";
bool isComplete = true;

---

3. Nullable Variables

Variables can be nullable (accept a null value) using ?:

int? nullableInt = null;

---

4. Type Inference with var

The var keyword allows the compiler to infer the variable’s type based on the assigned value:

var age = 25;          // Compiler infers as int
var name = "John";     // Compiler infers as string

Note: The type of a var variable cannot change once assigned.

---

5. Constants

Constants are variables whose values cannot change:

const double Pi = 3.14159;

---

6. Enumerations (Enums)

Enums represent a set of named constants:

enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
Days today = Days.Monday;

---

7. Reference Types vs Value Types

• Value Types: Store data directly (e.g., int, float, bool).
• Reference Types: Store references to the data (e.g., string, objects).

---

8. Type Casting

C# supports both implicit and explicit type casting.

Implicit Casting (Safe Conversion)

Automatically converts a smaller type to a larger type:

int num = 10;
double result = num; // Implicit cast

Explicit Casting (Type Conversion)

Manually converts a larger type to a smaller type:

double num = 9.78;
int result = (int)num; // Explicit cast

Convert Class

For additional control, use the Convert class:

string numStr = "25";
int num = Convert.ToInt32(numStr);

---

9. String Interpolation

You can combine strings and variables using $:

string name = "Alice";
int age = 25;
Console.WriteLine($"Name: {name}, Age: {age}");

---

10. Example Program Using Variables

using System;

class Program
{
    static void Main(string[] args)
    {
        int age = 30;
        double salary = 50000.50;
        string name = "John Doe";
        bool isEmployed = true;

        Console.WriteLine($"Name: {name}, Age: {age}, Salary: ${salary}, Employed: {isEmployed}");
    }
}

---

C# variables and data types offer flexibility, ensuring you can efficiently work with data. Let me know if you’d like further examples or advanced topics, such as custom classes or collections! 😊