Variables, Data Types, and Operators

Variables, Data Types, and Operators in C# 🚀

Understanding variables, data types, and operators is essential for writing C# programs. Let’s go step by step.

---

1️⃣ Variables in C#

A variable is a named storage location that holds data.

🔹 Declaring Variables

dataType variableName = value;

Example:

int age = 30;  
string name = "John";  
double price = 99.99;

🔹 Variable Naming Rules

• ✅ Must start with a letter or underscore (_)
• ✅ Can contain letters, digits, and underscores
• ✅ Case-sensitive (myVar and MyVar are different)
• ✅ Cannot use C# keywords (e.g., int, class, public)

---

2️⃣ Data Types in C#

C# has value types (stored directly in memory) and reference types (stored as references).

🔹 Common Value Types

Data Type	Size	Example	Description
int	4 bytes	int x = 100;	Stores whole numbers
double	8 bytes	double pi = 3.14;	Stores decimal numbers
float	4 bytes	float price = 9.99f;	Smaller decimal precision
char	2 bytes	char grade = 'A';	Stores a single character
bool	1 byte	bool isActive = true;	Stores true or false
decimal	16 bytes	decimal salary = 10000.50m;	High-precision financial calculations
long	8 bytes	long bigNumber = 1000000000L;	Stores large integers
short	2 bytes	short smallNum = 300;	Stores small whole numbers

🔹 Reference Types

Data Type	Example	Description
string	string message = "Hello";	Stores text
object	object obj = 42;	Can store any data type
dynamic	dynamic data = "text";	Type can change at runtime

---

3️⃣ Implicit and Explicit Type Conversion

🔹 Implicit Conversion (Safe)

int num = 10;
double result = num; // Implicit conversion (int → double)

🔹 Explicit Conversion (Casting)

double price = 99.99;
int roundedPrice = (int) price; // Explicit conversion (double → int)

🔹 Using Convert Class

string strNumber = "123";
int number = Convert.ToInt32(strNumber);

---

4️⃣ Operators in C#

Operators perform operations on variables and values.

🔹 Arithmetic Operators

Operator	Example	Description
+	a + b	Addition
-	a - b	Subtraction
*	a * b	Multiplication
/	a / b	Division
%	a % b	Modulus (remainder)

int a = 10, b = 5;
Console.WriteLine(a + b); // 15
Console.WriteLine(a - b); // 5
Console.WriteLine(a * b); // 50
Console.WriteLine(a / b); // 2
Console.WriteLine(a % b); // 0

🔹 Relational (Comparison) Operators

Operator	Example	Description
==	a == b	Equal to
!=	a != b	Not equal to
>	a > b	Greater than
<	a < b	Less than
>=	a >= b	Greater than or equal to
<=	a <= b	Less than or equal to

int x = 10, y = 5;
Console.WriteLine(x > y); // True
Console.WriteLine(x == y); // False
Console.WriteLine(x != y); // True

🔹 Logical Operators

Operator	Example	Description
&&	a && b	Logical AND
||	a || b	Logical OR
!	!a	Logical NOT

bool isSunny = true;
bool isWeekend = false;
Console.WriteLine(isSunny && isWeekend); // False
Console.WriteLine(isSunny || isWeekend); // True
Console.WriteLine(!isSunny); // False

🔹 Assignment Operators

Operator	Example	Equivalent To
=	a = b	Assign b to a
+=	a += b	a = a + b
-=	a -= b	a = a - b
*=	a *= b	a = a * b
/=	a /= b	a = a / b
%=	a %= b	a = a % b

int num = 10;
num += 5; // num = num + 5 (15)
num *= 2; // num = num * 2 (30)

🔹 Unary Operators

Operator	Example	Description
++	a++	Increment
--	a--	Decrement

int count = 5;
Console.WriteLine(count++); // 5 (Post-increment)
Console.WriteLine(++count); // 7 (Pre-increment)

---

5️⃣ Constants (const and readonly)

🔹 const (Compile-time constant) – Value must be assigned at declaration and cannot change.

const double PI = 3.14159;

🔹 readonly (Run-time constant) – Value can be assigned in constructor but cannot change afterward.

class Example {
    readonly int number;
    public Example() {
        number = 100; // Allowed
    }
}

---

🔚 Summary

• ✅ Variables store values and follow naming rules
• ✅ Data types include value types (int, double) and reference types (string, object)
• ✅ Implicit and explicit conversions help change data types
• ✅ Operators include arithmetic, relational, logical, and assignment operators