Control Flow: If-Else Statements

Welcome to the first lesson in C# Fundamentals! In this lesson, you’ll learn how to use if-else statements to make decisions in your programs. Let’s get started!

What Are If-Else Statements?

If-else statements allow your program to make decisions based on conditions. Depending on whether a condition is true or false, the program executes a specific block of code.

Key Point: Use if-else statements to control the flow of your program based on logic.

Syntax of If-Else Statements

The basic syntax of an if-else statement is:

if (condition) {

/* code to execute if condition is true */ }

else {

/* code to execute if condition is false */

}

Example:

using System;

class Program {
    static void Main() {
        int age = 20;

        if (age >= 18) {
            Console.WriteLine("You are an adult.");
        } else {
            Console.WriteLine("You are not an adult.");
        }
    }
}

Using Else-If

If you need to check multiple conditions, you can use else-if statements. Example:

Key Point: Use else-if to check additional conditions after the initial if statement.

using System;

class Program {
    static void Main() {
        int age = 20;

        if (age >= 18) {
            Console.WriteLine("You are an adult.");
        } else {
            Console.WriteLine("You are not an adult.");
        }
    }
}

Comparison Operators

If-else statements use comparison operators to evaluate conditions. Common operators include:

• ==: Equal to
• !=: Not equal to
• >: Greater than
• <: Less than
• >=: Greater than or equal to
• <=: Less than or equal to

Tip: Use the appropriate operator for your condition.

Logical Operators

You can combine conditions using logical operators:

• &&: Logical AND (true if both conditions are true).
• ||: Logical OR (true if at least one condition is true).
• !: Logical NOT (inverts the truth value).

Example:

using System;

class Program {
    static void Main() {
        int age = 25;
        bool hasLicense = true;

        if (age >= 18 && hasLicense) {
            Console.WriteLine("You can drive.");
        } else {
            Console.WriteLine("You cannot drive.");
        }
    }
}

Nesting If Statements

You can nest if statements inside each other for more complex conditions. Example:

Tip: Avoid excessive nesting to keep your code readable.

using System;

class Program {
    static void Main() {
        int age = 20;
        bool hasPermission = true;

        if (age >= 18) {
            if (hasPermission) {
                Console.WriteLine("Access granted.");
            } else {
                Console.WriteLine("Access denied. Permission required.");
            }
        } else {
            Console.WriteLine("Access denied. You must be 18 or older.");
        }
    }
}

Practice Challenge

Write a program that asks the user for their age and checks if they are eligible to vote. Example:

using System;

class Program {
    static void Main() {
        Console.WriteLine("Enter your age:");
        int age = int.Parse(Console.ReadLine());

        if (age >= 18) {
            Console.WriteLine("You are eligible to vote.");
        } else {
            Console.WriteLine("You are not eligible to vote.");
        }
    }
}

Great Job!

Congratulations! You’ve learned how to use if-else statements to make decisions in your C# programs. In the next lesson, we’ll explore loops and learn how to repeat tasks efficiently. Let’s keep coding!