Throw and rethrow patterns in C Sharp (C#) - Mini Project: Build & Apply

Throw and Rethrow Patterns

📖 Scenario: Imagine you are building a simple calculator app that divides two numbers. Sometimes, the user might enter zero as the divisor, which causes an error. You want to catch this error, add a message, and then rethrow it so the program can handle it properly.

🎯 Goal: You will create a program that demonstrates how to throw and rethrow exceptions in C#. This helps you understand how to handle errors and pass them along with extra information.

📋 What You'll Learn

Create a method called Divide that takes two integers numerator and denominator.

Inside Divide, throw a DivideByZeroException if denominator is zero.

Use a try-catch block in Divide to catch the exception, add a message, and rethrow it.

In Main, call Divide and catch the rethrown exception to print its message.

💡 Why This Matters

🌍 Real World

Throwing and rethrowing exceptions is common in real apps to handle errors clearly and pass useful messages up the call chain.

💼 Career

Understanding exception handling is essential for writing robust, maintainable code in professional software development.

1

Create the Divide method with parameters

Create a method called Divide that takes two integer parameters named numerator and denominator. For now, just return 0 inside the method.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
    }

    // Create the Divide method with two int parameters
    static int Divide(int numerator, int denominator)
    {
        // Your code here
        return 0;
    }
}

Need a hint?

Define a method named Divide with two int parameters and return an int value.

2

Throw DivideByZeroException if denominator is zero

Inside the Divide method, add an if statement to check if denominator is zero. If it is, throw a new DivideByZeroException with the message "Cannot divide by zero."

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
    }

    static int Divide(int numerator, int denominator)
    {
        // Throw exception if denominator is zero
        if (denominator == 0)
        {
            // Your code here
        }
        return 0;
    }
}

Need a hint?

Use throw new DivideByZeroException with the exact message inside the if block.

3

Catch and rethrow the exception with a message

Modify the Divide method to use a try-catch block. Put the if check and division inside the try. In the catch (DivideByZeroException ex), throw a new DivideByZeroException with the message "Error in Divide method: " plus the original exception message.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
    }

    static int Divide(int numerator, int denominator)
    {
        try
        {
            // Your code here
        }
        catch (DivideByZeroException ex)
        {
            // Your code here
        }
    }
}

Need a hint?

Use try-catch to catch the exception and rethrow with a new message combining your text and ex.Message.

4

Call Divide in Main and print the exception message

In the Main method, call Divide(10, 0) inside a try-catch block. Catch DivideByZeroException ex and print ex.Message using Console.WriteLine.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        // Your code here
    }

    static int Divide(int numerator, int denominator)
    {
        try
        {
            if (denominator == 0)
            {
                throw new DivideByZeroException("Cannot divide by zero.");
            }
            return numerator / denominator;
        }
        catch (DivideByZeroException ex)
        {
            throw new DivideByZeroException("Error in Divide method: " + ex.Message);
        }
    }
}

Need a hint?

Use try-catch in Main to call Divide and print the exception message.