Multiple catch blocks in C Sharp (C#)

Introduction

Multiple catch blocks let you handle different errors in different ways. This helps your program respond correctly to each problem.

When you want to handle different types of errors separately.

When you want to show different messages for different problems.

When you want to fix or log errors differently based on their type.

When you want to keep your program running smoothly after an error.

When you want to avoid one big catch that hides the real problem.

Syntax

C Sharp (C#)

try
{
    // code that might cause an error
}
catch (ExceptionType1 ex1)
{
    // handle ExceptionType1
}
catch (ExceptionType2 ex2)
{
    // handle ExceptionType2
}
catch (Exception ex)
{
    // handle any other exceptions
}

Each catch block handles a specific type of error.

The last catch block can catch any error not caught before.

Examples

This example catches a specific error when accessing an array out of bounds, and a general error for anything else.

C Sharp (C#)

try
{
    int[] numbers = {1, 2, 3};
    Console.WriteLine(numbers[5]);
}
catch (IndexOutOfRangeException ex)
{
    Console.WriteLine("Index is out of range.");
}
catch (Exception ex)
{
    Console.WriteLine("Some other error happened.");
}

This example catches format errors when converting text to number, and any other errors separately.

C Sharp (C#)

try
{
    int x = int.Parse("abc");
}
catch (FormatException ex)
{
    Console.WriteLine("Input was not a number.");
}
catch (Exception ex)
{
    Console.WriteLine("Unknown error.");
}

Sample Program

This program asks the user for a number, tries to divide 10 by it, and handles three types of errors: wrong input format, division by zero, and any other unexpected errors.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        try
        {
            Console.WriteLine("Enter a number:");
            string input = Console.ReadLine();
            int number = int.Parse(input);
            int result = 10 / number;
            Console.WriteLine($"10 divided by {number} is {result}");
        }
        catch (FormatException)
        {
            Console.WriteLine("That was not a valid number.");
        }
        catch (DivideByZeroException)
        {
            Console.WriteLine("Cannot divide by zero.");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Unexpected error: {ex.Message}");
        }
    }
}

Important Notes

Order matters: catch more specific exceptions before general ones.

You can have as many catch blocks as needed.

Use the exception object (like ex) to get more info if needed.

Summary

Multiple catch blocks let you handle different errors in different ways.

Put specific exceptions first, then general ones last.

This helps your program stay clear and respond well to problems.

Practice

1.

What is the main purpose of using multiple catch blocks in C#?

easy

A. To avoid using try blocks

B. To handle different types of exceptions separately

C. To make the code run faster

D. To declare multiple variables

Solution

1. Step 1: Understand the role of catch blocks

   catch blocks are used to handle errors that happen in the try block.

2. Step 2: Recognize why multiple catch blocks are used

   Using multiple catch blocks lets you respond differently to different error types, making your program clearer and safer.

3. Final Answer:

   To handle different types of exceptions separately -> Option B

4. Quick Check:

   Multiple catch blocks = handle different exceptions [OK]

Hint: Multiple catch blocks handle different errors separately [OK]

Common Mistakes:

• Thinking multiple catch blocks speed up code
• Believing catch blocks replace try blocks
• Using catch blocks to declare variables

2.

Which of the following is the correct syntax order for multiple catch blocks in C#?

try { ... }
catch (ArgumentNullException e) { ... }
catch (Exception e) { ... }

easy

A. Specific exceptions first, general exceptions last

B. General exceptions first, specific exceptions last

C. Order does not matter

D. Only one catch block is allowed

Solution

1. Step 1: Understand exception hierarchy

   Specific exceptions like ArgumentNullException inherit from general exceptions like Exception.

2. Step 2: Order catch blocks correctly

   Place specific exceptions first so they catch their errors before the general catch block handles all others.

3. Final Answer:

   Specific exceptions first, general exceptions last -> Option A

4. Quick Check:

   Specific before general catch blocks [OK]

Hint: Put specific exceptions before general ones in catch blocks [OK]

Common Mistakes:

• Placing general catch before specific causes unreachable code
• Assuming catch order does not matter
• Trying to use multiple catch blocks without try

3.

What will be the output of this C# code?

try {
    int[] arr = new int[2];
    Console.WriteLine(arr[5]);
} catch (IndexOutOfRangeException) {
    Console.WriteLine("Index error caught");
} catch (Exception) {
    Console.WriteLine("General error caught");
}

medium

A. No output, program crashes

B. General error caught

C. Index error caught

D. Compilation error

Solution

1. Step 1: Identify the exception thrown

   Accessing arr[5] causes an IndexOutOfRangeException because the array size is 2.

2. Step 2: Match exception to catch block

   The first catch block matches IndexOutOfRangeException, so it runs and prints "Index error caught".

3. Final Answer:

   Index error caught -> Option C

4. Quick Check:

   IndexOutOfRangeException triggers first catch [OK]

Hint: Exception type matches first suitable catch block [OK]

Common Mistakes:

• Thinking general catch runs before specific
• Assuming no exception occurs
• Confusing exception types

4.

Find the error in this code snippet:

try {
    int x = int.Parse("abc");
} catch (Exception e) {
    Console.WriteLine("General error");
} catch (FormatException e) {
    Console.WriteLine("Format error");
}

medium

A. The FormatException catch block is unreachable

B. Missing finally block

C. Try block syntax is incorrect

D. No error, code is correct

Solution

1. Step 1: Check catch block order

   The first catch block catches all Exception types, including FormatException.

2. Step 2: Identify unreachable catch block

   Since Exception catch is first, the FormatException catch block can never run, causing a compile error.

3. Final Answer:

   The FormatException catch block is unreachable -> Option A

4. Quick Check:

   General catch before specific causes unreachable code [OK]

Hint: Place specific catch blocks before general ones to avoid unreachable code [OK]

Common Mistakes:

• Putting general catch before specific
• Ignoring unreachable code errors
• Thinking finally block is mandatory

5.

You want to handle NullReferenceException and DivideByZeroException differently, but also catch any other exceptions generally. Which is the best order of catch blocks?

try {
    // code that may throw exceptions
} catch (___) {
    Console.WriteLine("Null reference error");
} catch (___) {
    Console.WriteLine("Divide by zero error");
} catch (___) {
    Console.WriteLine("Other error");
}

hard

A. Exception, DivideByZeroException, NullReferenceException

B. Exception, NullReferenceException, DivideByZeroException

C. DivideByZeroException, Exception, NullReferenceException

D. NullReferenceException, DivideByZeroException, Exception

Solution

1. Step 1: Identify specific exceptions

   NullReferenceException and DivideByZeroException are specific exceptions to catch first.

2. Step 2: Place general exception last

   The general Exception catch block should come last to catch all other exceptions.

3. Final Answer:

   NullReferenceException, DivideByZeroException, Exception -> Option D

4. Quick Check:

   Specific exceptions first, general last [OK]

Hint: Catch specific exceptions before general Exception last [OK]

Common Mistakes:

• Putting Exception catch first
• Mixing order of specific exceptions
• Omitting general catch block