Lesson 5: Conditional Statements (if, else if, else) in C#

Welcome to Lesson 5! In this lesson, we’ll explore conditional statements in C#, which allow your programs to make decisions based on certain conditions. Conditional statements are essential for controlling the flow of execution in your applications. We’ll cover the if, else if, and else statements, and how to use them to create logical branches in your code.

1. The if Statement

The if statement is used to execute a block of code only if a specified condition is true. It’s the simplest form of conditional statement.

Syntax:

if (condition)
{
    // Code to execute if the condition is true
}

Example:

int temperature = 30;

if (temperature > 25)
{
    Console.WriteLine("It's a hot day!");
}

Explanation:

• The condition checks if temperature is greater than 25. If true, it prints “It’s a hot day!” to the console.

2. The else Statement

The else statement follows an if statement and is executed when the if condition is false. It provides an alternative block of code to execute when the initial condition isn’t met.

Syntax:

if (condition)
{
    // Code to execute if the condition is true
}
else
{
    // Code to execute if the condition is false
}

Example:

int age = 18;

if (age >= 18)
{
    Console.WriteLine("You are an adult.");
}
else
{
    Console.WriteLine("You are a minor.");
}

Explanation:

• The condition checks if age is 18 or older. If true, it prints “You are an adult.” Otherwise, it prints “You are a minor.”

3. The else if Statement

The else if statement allows you to check multiple conditions sequentially. It’s used when you need to evaluate more than two conditions.

Syntax:

if (condition1)
{
    // Code to execute if condition1 is true
}
else if (condition2)
{
    // Code to execute if condition2 is true
}
else
{
    // Code to execute if none of the above conditions are true
}

Example:

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: D or below");
}

Explanation:

• The program checks the score and prints the appropriate grade based on the value. If none of the conditions match, it falls through to the else block.

4. Nested Conditional Statements

You can nest if statements within other if statements to handle more complex logic.

Example:

int number = 45;

if (number > 0)
{
    if (number % 2 == 0)
    {
        Console.WriteLine("The number is positive and even.");
    }
    else
    {
        Console.WriteLine("The number is positive and odd.");
    }
}
else
{
    Console.WriteLine("The number is zero or negative.");
}

Explanation:

• The outer if checks if number is positive. If true, it further checks if the number is even or odd with an inner if.

5. Combining Conditions

You can combine multiple conditions using logical operators such as && (AND) and || (OR) in your if statements.

Example:

int age = 25;
bool hasLicense = true;

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

Explanation:

• The condition checks if both age is 18 or older and hasLicense is true. If both conditions are met, it prints “You are eligible to drive.” Otherwise, it prints “You are not eligible to drive.”

6. Example: Putting It All Together

Here’s a comprehensive example demonstrating the use of if, else if, and else statements:

Code Example:

using System;

class Program
{
    static void Main()
    {
        int score = 78;
        bool hasPassed = true;

        if (score >= 90)
        {
            Console.WriteLine("Excellent!");
        }
        else if (score >= 80)
        {
            Console.WriteLine("Good job!");
        }
        else if (score >= 70)
        {
            Console.WriteLine("Well done!");
        }
        else
        {
            Console.WriteLine("Needs improvement.");
        }

        if (hasPassed)
        {
            Console.WriteLine("Congratulations on passing!");
        }
        else
        {
            Console.WriteLine("Sorry, you did not pass.");
        }
    }
}

Explanation:

• The first set of if, else if, and else statements evaluates the score and provides feedback.
• The second if statement checks if the hasPassed condition is true and prints an appropriate message.

Summary

In this lesson, you learned how to use if, else if, and else statements in C# to make decisions in your code. Conditional statements are powerful tools for controlling the flow of execution based on various conditions. We also explored nesting and combining conditions to handle more complex scenarios.

Happy coding!