Variables store data your program uses. Each variable has a type that tells C# what kind of data it holds.
📦 Declaring Variables
1
2
3
4
5
| int age = 25; // Integer
double price = 19.99; // Decimal number
string name = "Alice"; // Text
bool isActive = true; // True/False
char letter = 'A'; // Single character
|
🧮 Operators
Operators in C#
C# provides several types of operators to perform operations on variables:
Arithmetic Operators
| Operator |
Description |
Example |
+ |
Addition |
a + b |
- |
Subtraction |
a - b |
* |
Multiplication |
a * b |
/ |
Division |
a / b |
% |
Modulus (remainder) |
a % b |
Assignment Operators
| Operator |
Example |
Equivalent To |
= |
a = 5 |
|
+= |
a += 2 |
a = a + 2 |
-= |
a -= 2 |
a = a - 2 |
*= |
a *= 2 |
a = a * 2 |
/= |
a /= 2 |
a = a / 2 |
%= |
a %= 2 |
a = a % 2 |
Comparison Operators
| Operator |
Description |
Example |
== |
Equal to |
a == b |
!= |
Not equal to |
a != b |
< |
Less than |
a < b |
> |
Greater than |
a > b |
<= |
Less than or equal |
a <= b |
>= |
Greater than or equal |
a >= b |
Logical Operators
| Operator |
Description |
Example |
&& |
Logical AND |
a && b |
|| |
Logical OR |
a || b |
! |
Logical NOT |
!a |
Bitwise Operators
| Operator |
Description |
Example |
& |
Bitwise AND |
a & b |
| |
Bitwise OR |
a | b |
^ |
Bitwise XOR |
a ^ b |
~ |
Bitwise NOT |
~a |
<< |
Left shift |
a << 2 |
>> |
Right shift |
a >> 2 |
Math Functions in C#
C# provides the System.Math class for common math operations:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
| using System;
double x = -3.7;
Console.WriteLine(Math.Abs(x)); // Absolute value: 3.7
Console.WriteLine(Math.Ceiling(x)); // Ceiling: -3
Console.WriteLine(Math.Floor(x)); // Floor: -4
Console.WriteLine(Math.Round(x)); // Round: -4
Console.WriteLine(Math.Sqrt(16)); // Square root: 4
Console.WriteLine(Math.Pow(2, 3)); // 2 to the power 3: 8
Console.WriteLine(Math.Max(3, 7)); // Maximum: 7
Console.WriteLine(Math.Min(3, 7)); // Minimum: 3
Console.WriteLine(Math.Sign(x)); // Sign: -1
Console.WriteLine(Math.Truncate(x)); // Truncate: -3
Console.WriteLine(Math.Log(10)); // Natural log: 2.3025...
Console.WriteLine(Math.Log10(100)); // Base-10 log: 2
Console.WriteLine(Math.Exp(2)); // Exponential: e^2
Console.WriteLine(Math.Sin(Math.PI/2)); // Sine: 1
Console.WriteLine(Math.Cos(0)); // Cosine: 1
Console.WriteLine(Math.Tan(0)); // Tangent: 0
|
Note: To generate random numbers, use the Random class, not Math.
Example:
1
2
| var rnd = new Random();
int randomNumber = rnd.Next(1, 101); // 1 to 100 inclusive
|
📝 Type Inference
You can let C# figure out the type:
1
2
| var city = "London"; // C# knows this is a string
var number = 10; // C# knows this is an int
|
⚠️ Good Practices
- Use clear, descriptive names:
userName, totalPrice
- Pick the right type, don’t store numbers in a
string!
💡 Try It!
Write a program that asks for a user’s name and age, then prints a greeting:
1
2
3
4
5
| Console.Write("Enter your name: ");
string? name = Console.ReadLine();
Console.Write("Enter your age: ");
int age = int.Parse(Console.ReadLine() ?? "0");
Console.WriteLine($"Hi, {name}! You are {age} years old.");
|
Next: Learn about strong typing and type inference in C#.
