C# — Operators

Arithmetic operators

using System;

int a = 10, b = 3;

Console.WriteLine($"Add: {a + b}");   // 13
Console.WriteLine($"Sub: {a - b}");   // 7
Console.WriteLine($"Mul: {a * b}");   // 30
Console.WriteLine($"Div: {a / b}");   // 3 (integer)
Console.WriteLine($"Mod: {a % b}");   // 1

Increment and decrement

using System;

int x = 5;
Console.WriteLine(x++); // 5 (post-increment)
Console.WriteLine(++x); // 7 (pre-increment)
Console.WriteLine(x--); // 7 (post-decrement)
Console.WriteLine(--x); // 5 (pre-decrement)

Relational operators

using System;

Console.WriteLine(5 == 5);  // True
Console.WriteLine(5 != 3);  // True
Console.WriteLine(5 > 3);   // True
Console.WriteLine(5 < 3);   // False
Console.WriteLine(5 >= 5);  // True
Console.WriteLine(5 <= 3);  // False

Logical operators

using System;

bool a = true, b = false;

Console.WriteLine(a && b);  // False (AND)
Console.WriteLine(a || b);  // True  (OR)
Console.WriteLine(!a);      // False (NOT)

Null-coalescing operators

using System;

string? name = null;

// ?? operator
string displayName = name ?? "Anonymous";
Console.WriteLine(displayName); // Anonymous

// ??= operator (C# 8+)
name ??= "Default";
Console.WriteLine(name); // Default

// ?. operator (null-conditional)
string? text = "Hello";
int? length = text?.Length;
Console.WriteLine(length); // 5

// ?.[] operator
string[]? arr = null;
char? first = arr?[0];
Console.WriteLine(first); // null

Pattern matching

using System;

// is pattern
object obj = 42;
if (obj is int number)
{
    Console.WriteLine($"It's an int: {number}");
}

// switch pattern
string Describe(object obj) => obj switch
{
    int i when i > 0 => $"Positive int: {i}",
    int i => $"Non-positive int: {i}",
    string s => $"String: {s}",
    null => "Null",
    _ => "Unknown"
};

Console.WriteLine(Describe(42));
Console.WriteLine(Describe("hello"));

Ternary operator

using System;

int age = 20;
string status = (age >= 18) ? "Adult" : "Minor";
Console.WriteLine(status); // Adult

String operators

using System;

// Concatenation
string first = "Hello";
string second = "World";
string result = first + " " + second;
Console.WriteLine(result); // Hello World

// Interpolation
string name = "Alice";
Console.WriteLine($"Hello, {name}!");

// Repetition (C# has no * operator for strings)
string line = new string('-', 20);
Console.WriteLine(line); // --------------------

typeof and sizeof

using System;

Console.WriteLine(typeof(int));     // System.Int32
Console.WriteLine(typeof(string));  // System.String

Console.WriteLine(sizeof(int));     // 4
Console.WriteLine(sizeof(double));  // 8

is operator

using System;

Console.WriteLine(42 is int);           // True
Console.WriteLine("hi" is string);      // True
Console.WriteLine(3.14 is double);      // True

// Type pattern
if (42 is int n)
{
    Console.WriteLine($"Matched: {n}");
}

Best practices

• Use ?. and ?? for null-safe code
• Prefer pattern matching over type casting
• Use is for type checking, not GetType() ==
• Always use parentheses for clarity in complex expressions

Mini Practice

Write C# code that:

1. Uses null-coalescing and null-conditional operators
2. Demonstrates pattern matching with switch
3. Shows the difference between == and is
4. Uses string interpolation with format specifiers

Up Next

In the next lesson, you'll learn about Strings — working with System.String in C#.