Operators

Lesson 3 • Beginner Track

What You'll Learn

Use arithmetic operators (+, -, *, /, %) and understand integer division
Apply increment (++), decrement (--), and compound assignment (+=, *=)
Compare values with ==, !=, >, <, >=, <= and understand what they return
Combine conditions with logical operators (&&, ||, !)
Use the ternary operator for concise conditional expressions
Handle null values safely with ??, ??=, and ?. operators

💡 Real-World Analogy

Operators are like the buttons on a calculator. Arithmetic operators (+, -, ×, ÷) do maths. Comparison operators are like a referee making yes/no decisions — "Is player A's score higher than player B's?" Logical operators are like combining conditions on a checklist: "Do you have BOTH a passport AND a visa?" (&&) or "Do you have EITHER cash OR a card?" (||).

📊 Operator Precedence

Priority	Operators	Example
1 (Highest)	() ?. !	Parentheses, null-conditional, not
2	* / %	Multiply, divide, remainder
3	+ -	Add, subtract
4	< > <= >=	Comparison
5	== !=	Equality
6	&&	Logical AND
7	\|\|	Logical OR
8 (Lowest)	= += -= *= ??=	Assignment

1. Arithmetic Operators

Arithmetic operators perform mathematical calculations. Watch out for integer division — 10 / 3 gives 3, not 3.33. Use ++ and -- for incrementing/decrementing, and compound operators like += for concise updates.

Arithmetic Operators

Explore arithmetic, increment/decrement, and compound assignment.

Try it Yourself »

using System;

class Program
{
    static void Main()
    {
        int a = 10, b = 3;

        // Basic arithmetic
        Console.WriteLine($"a + b = {a + b}");   // 13
        Console.WriteLine($"a - b = {a - b}");   // 7
        Console.WriteLine($"a * b = {a * b}");   // 30
        Console.WriteLine($"a / b = {a / b}");   // 3 (integer division!)
        Console.WriteLine($"a % b = {a % b}");   // 1 (remainder)

        // Increment & decrement
        int x = 5;
        Console.WriteLine($
...

2. Comparison & Logical Operators

Comparison operators return bool (true/false). Logical operators combine multiple conditions: && requires both to be true, || requires at least one, and ! flips the result. These are the foundation of control flow.

Comparison & Logical Operators

Compare values and combine conditions with &&, ||, and !.

Try it Yourself »

using System;

class Program
{
    static void Main()
    {
        // Comparison operators
        int age = 20;
        Console.WriteLine($"age == 20: {age == 20}");  // true
        Console.WriteLine($"age != 18: {age != 18}");  // true
        Console.WriteLine($"age > 18:  {age > 18}");   // true
        Console.WriteLine($"age <= 21: {age <= 21}");   // true

        // Logical operators
        bool hasTicket = true;
        bool isVIP = false;

        // AND — both must be true
        
...

3. Ternary & Null-Safe Operators

The ternary operator (condition ? a : b) is a one-line if-else. C# also has powerful null-safe operators: ?? provides a fallback for null values, ??= assigns only if null, and ?. safely accesses members without crashing on null.

Ternary & Null Operators

Use ternary expressions and handle null values safely.

Try it Yourself »

using System;

class Program
{
    static void Main()
    {
        // Null-coalescing operator (??)
        string? userName = null;
        string displayName = userName ?? "Guest";
        Console.WriteLine($"Welcome, {displayName}!");  // "Guest"

        userName = "Alice";
        displayName = userName ?? "Guest";
        Console.WriteLine($"Welcome, {displayName}!");  // "Alice"

        // Null-coalescing assignment (??=)
        string? city = null;
        city ??= "London";  // Assig
...

Pro Tips

💡 Use parentheses for clarity: Even if precedence is correct, (a > 5) && (b < 10) is clearer than a > 5 && b < 10.
💡 Prefer ?? over if-null checks: string name = input ?? "default"; is cleaner than a 4-line if-else.
💡 Short-circuit evaluation: && and || stop evaluating as soon as the result is known. Put cheaper checks first.
💡 Use ?. to avoid NullReferenceException: user?.Address?.City returns null safely instead of crashing.

Common Mistakes

Using = instead of ==: if (x = 5) is assignment, not comparison. C# catches this for bools but be careful.
Integer division surprise: 7 / 2 gives 3. Cast one operand: (double)7 / 2 gives 3.5.
Confusing ++ placement: x++ returns the old value then increments. ++x increments first then returns the new value.
Ignoring null warnings: C# 8+ has nullable reference types. Don't suppress warnings with ! — use ?? or ?. instead.
Chaining comparisons: 1 < x < 10 doesn't work like maths. Use x > 1 && x < 10.

🎉 Lesson Complete

✅ Arithmetic: +, -, *, /, % — integer division truncates
✅ Increment/decrement: x++ (post) vs ++x (pre) — different return values
✅ Comparison operators return bool: ==, !=, >, <, >=, <=
✅ Logical: && (AND), || (OR), ! (NOT) — short-circuit evaluation
✅ Ternary: condition ? valueIfTrue : valueIfFalse
✅ Null-safe: ?? (fallback), ??= (assign if null), ?. (safe access)
✅ Next lesson: Control Flow — if statements, switch, and pattern matching

Operators

What You'll Learn

💡 Real-World Analogy

📊 Operator Precedence

1. Arithmetic Operators

Arithmetic Operators

2. Comparison & Logical Operators

Comparison & Logical Operators

3. Ternary & Null-Safe Operators

Ternary & Null Operators

Pro Tips

Common Mistakes

🎉 Lesson Complete

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