If, Else If, and Else Statements

Conditional statements allow your program to make decisions based on conditions. This is how you control the flow of your program.

The if Statement

The if statement executes code only when a condition is true:


csharp
1int age = 20;
2
3if (age >= 18)
4{
5    Console.WriteLine("You are an adult.");
6}

Syntax


csharp
1if (condition)
2{
3    // Code to execute when condition is true
4}

The condition must be a boolean expression (evaluates to true or false).

The else Statement

The else statement provides an alternative when the condition is false:


csharp
1int age = 16;
2
3if (age >= 18)
4{
5    Console.WriteLine("You are an adult.");
6}
7else
8{
9    Console.WriteLine("You are a minor.");
10}

Output

You are a minor.

The else if Statement

Use else if to check multiple conditions:


csharp
1int score = 85;
2
3if (score >= 90)
4{
5    Console.WriteLine("Grade: A");
6}
7else if (score >= 80)
8{
9    Console.WriteLine("Grade: B");
10}
11else if (score >= 70)
12{
13    Console.WriteLine("Grade: C");
14}
15else if (score >= 60)
16{
17    Console.WriteLine("Grade: D");
18}
19else
20{
21    Console.WriteLine("Grade: F");
22}

Output

Grade: B

How It Works

Conditions are checked from top to bottom
The first true condition's code block executes
Remaining conditions are skipped
else is optional and catches everything else

Nested if Statements

You can put if statements inside other if statements:


csharp
1bool isLoggedIn = true;
2bool isAdmin = true;
3
4if (isLoggedIn)
5{
6    Console.WriteLine("Welcome!");
7
8    if (isAdmin)
9    {
10        Console.WriteLine("You have admin access.");
11    }
12    else
13    {
14        Console.WriteLine("You have standard access.");
15    }
16}
17else
18{
19    Console.WriteLine("Please log in.");
20}

Avoiding Deep Nesting

Deep nesting can be hard to read. Consider restructuring:


csharp
1// Hard to read
2if (condition1)
3{
4    if (condition2)
5    {
6        if (condition3)
7        {
8            // Do something
9        }
10    }
11}
12
13// Better: combine conditions
14if (condition1 && condition2 && condition3)
15{
16    // Do something
17}
18
19// Or: use early returns
20if (!condition1) return;
21if (!condition2) return;
22if (!condition3) return;
23// Do something

Braces and Single Statements

For single statements, braces are optional (but recommended):


csharp
1// Without braces (works but not recommended)
2if (age >= 18)
3    Console.WriteLine("Adult");
4else
5    Console.WriteLine("Minor");
6
7// With braces (recommended)
8if (age >= 18)
9{
10    Console.WriteLine("Adult");
11}
12else
13{
14    Console.WriteLine("Minor");
15}

Always use braces to avoid bugs when adding more code later.

Common Patterns

Validation


csharp
1Console.Write("Enter your age: ");
2string input = Console.ReadLine() ?? "";
3
4if (int.TryParse(input, out int age))
5{
6    if (age < 0 || age > 150)
7    {
8        Console.WriteLine("Please enter a valid age.");
9    }
10    else
11    {
12        Console.WriteLine($"You are {age} years old.");
13    }
14}
15else
16{
17    Console.WriteLine("That's not a number.");
18}

Range Checking


csharp
1int temperature = 72;
2
3if (temperature < 32)
4{
5    Console.WriteLine("Freezing!");
6}
7else if (temperature < 60)
8{
9    Console.WriteLine("Cold");
10}
11else if (temperature < 80)
12{
13    Console.WriteLine("Comfortable");
14}
15else
16{
17    Console.WriteLine("Hot!");
18}

Null Checking


csharp
1string? name = GetUserName();  // Might return null
2
3if (name == null)
4{
5    Console.WriteLine("Name not provided");
6}
7else if (name.Length == 0)
8{
9    Console.WriteLine("Name is empty");
10}
11else
12{
13    Console.WriteLine($"Hello, {name}!");
14}
15
16// Or use string.IsNullOrEmpty
17if (string.IsNullOrEmpty(name))
18{
19    Console.WriteLine("Name not provided or empty");
20}

Boolean Variables in Conditions

You don't need == true for boolean variables:


csharp
1bool isActive = true;
2
3// Unnecessary
4if (isActive == true)
5{
6    Console.WriteLine("Active");
7}
8
9// Clean
10if (isActive)
11{
12    Console.WriteLine("Active");
13}
14
15// Checking for false
16if (!isActive)
17{
18    Console.WriteLine("Inactive");
19}

Practical Example


csharp
1Console.WriteLine("=== Movie Ticket Price Calculator ===");
2Console.Write("Enter your age: ");
3
4if (!int.TryParse(Console.ReadLine(), out int age))
5{
6    Console.WriteLine("Invalid age!");
7    return;
8}
9
10Console.Write("Is it a matinee showing? (yes/no): ");
11string matineeInput = Console.ReadLine()?.ToLower() ?? "";
12bool isMatinee = matineeInput == "yes" || matineeInput == "y";
13
14decimal price;
15
16if (age < 3)
17{
18    price = 0;
19    Console.WriteLine("Free admission for children under 3!");
20}
21else if (age < 12)
22{
23    price = isMatinee ? 6.00m : 8.00m;
24    Console.WriteLine("Child ticket");
25}
26else if (age >= 65)
27{
28    price = isMatinee ? 7.00m : 9.00m;
29    Console.WriteLine("Senior discount applied");
30}
31else
32{
33    price = isMatinee ? 9.00m : 12.00m;
34    Console.WriteLine("Adult ticket");
35}
36
37Console.WriteLine($"Ticket price: {price:C}");

Summary

In this lesson, you learned:

if executes code when a condition is true
else provides an alternative path
else if checks multiple conditions in sequence
Conditions are checked top to bottom; first match wins
Avoid deep nesting for readability
Always use braces for clarity

Next, we'll learn about the ternary operator for simple conditional expressions.