C# — If Else

Basic if statement

using System;

int temperature = 28;

if (temperature > 25)
{
    Console.WriteLine("It's warm outside!");
}

if-else

using System;

int hour = 14;

if (hour < 12)
{
    Console.WriteLine("Good morning!");
}
else
{
    Console.WriteLine("Good afternoon!");
}

if-else if-else

using System;

int score = 85;

if (score >= 90)
{
    Console.WriteLine("Grade: A");
}
else if (score >= 80)
{
    Console.WriteLine("Grade: B");
}
else if (score >= 70)
{
    Console.WriteLine("Grade: C");
}
else
{
    Console.WriteLine("Grade: F");
}

Ternary operator

using System;

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

Switch expression (C# 8+)

using System;

int day = 3;

string dayName = day switch
{
    1 => "Monday",
    2 => "Tuesday",
    3 => "Wednesday",
    4 => "Thursday",
    5 => "Friday",
    6 => "Saturday",
    7 => "Sunday",
    _ => "Invalid day"
};

Console.WriteLine(dayName); // Wednesday

Pattern matching in switch

using System;

object obj = 42;

string description = obj switch
{
    int i when i > 0 => $"Positive int: {i}",
    int i => $"Non-positive int: {i}",
    string s => $"String of length {s.Length}",
    null => "Null",
    _ => "Unknown type"
};

Console.WriteLine(description);

Type pattern matching

using System;

static string Describe(object obj)
{
    return obj switch
    {
        int n when n > 0 => $"Positive: {n}",
        int => "Non-positive integer",
        string s => $"String: \"{s}\"",
        bool b => b ? "True" : "False",
        double d => $"Double: {d}",
        null => "Null",
        _ => $"Other: {obj.GetType().Name}"
    };
}

Console.WriteLine(Describe(42));     // Positive: 42
Console.WriteLine(Describe("Hi"));  // String: "Hi"
Console.WriteLine(Describe(null));  // Null

Property pattern

using System;

record Person(string Name, int Age);

string Classify(Person p) => p switch
{
    { Age: < 13 } => "Child",
    { Age: < 18 } => "Teenager",
    { Age: < 65 } => "Adult",
    _ => "Senior"
};

Console.WriteLine(Classify(new("Alice", 30))); // Adult
Console.WriteLine(Classify(new("Bob", 10)));   // Child

Combining conditions

using System;

int age = 25;
int income = 50000;

if (age >= 18 && income >= 30000)
{
    Console.WriteLine("Qualifies for premium card.");
}

if (age < 12 || age > 65)
{
    Console.WriteLine("Discounted ticket.");
}

bool isBanned = false;
if (!isBanned)
{
    Console.WriteLine("Access granted.");
}

If with declaration (C# 8+)

using System;

// Declare variable in if condition
if (int.TryParse("42", out int result))
{
    Console.WriteLine($"Parsed: {result}");
}

// Also works with pattern matching
if ("hello" is string { Length: > 3 } s)
{
    Console.WriteLine($"Long string: {s}");
}

Best practices

• Use pattern matching instead of type checking + casting
• Use switch expressions for cleaner code
• Prefer early returns to reduce nesting
• Use is for null checking

Mini Practice

Write C# code that:

1. Uses a switch expression to classify a number
2. Demonstrates pattern matching with when clauses
3. Uses if with variable declaration
4. Combines conditions with && and ||

Up Next

In the next lesson, you'll learn about Loops — for, foreach, while, and do-while.