Multiple catch blocks in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of multiple catch blocks with specific exceptions

What is the output of this C# code when an IndexOutOfRangeException is thrown?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        try {
            int[] arr = new int[2];
            Console.WriteLine(arr[5]);
        }
        catch (NullReferenceException) {
            Console.WriteLine("Null reference caught");
        }
        catch (IndexOutOfRangeException) {
            Console.WriteLine("Index out of range caught");
        }
        catch (Exception) {
            Console.WriteLine("General exception caught");
        }
    }
}

A Index out of range caught

B No output, program crashes

C Null reference caught

D General exception caught

💡 Hint

Think about which catch block matches the thrown exception type exactly.

The thrown exception is IndexOutOfRangeException, so the catch block for that specific exception runs, printing "Index out of range caught".

❓ Predict Output

intermediate

Which catch block executes for a NullReferenceException?

Given this code, what will be printed when a NullReferenceException occurs?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        try {
            string s = null;
            Console.WriteLine(s.Length);
        }
        catch (ArgumentException) {
            Console.WriteLine("Argument exception caught");
        }
        catch (NullReferenceException) {
            Console.WriteLine("Null reference caught");
        }
        catch (Exception) {
            Console.WriteLine("General exception caught");
        }
    }
}

A No output, program crashes

B General exception caught

C Argument exception caught

D Null reference caught

💡 Hint

Which catch block matches the exception type exactly?

NullReferenceException is caught by the matching catch block, so it prints "Null reference caught".

❓ Predict Output

advanced

Output when multiple catch blocks could match

What will this code print when a FormatException is thrown?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        try {
            int.Parse("abc");
        }
        catch (FormatException) {
            Console.WriteLine("Format exception caught");
        }
        catch (Exception) {
            Console.WriteLine("General exception caught");
        }
    }
}

A Format exception caught

B No output, program crashes

C Compilation error due to catch order

D General exception caught

💡 Hint

Check the order of catch blocks and C# rules about exception handling.

In C#, catch blocks must be ordered from most specific to most general. Catching Exception before FormatException causes a compile-time error.

❓ Predict Output

advanced

Which catch block handles AggregateException?

What will be printed when this code throws an AggregateException?

C Sharp (C#)

using System;
using System.Threading.Tasks;

class Program {
    static void Main() {
        try {
            Task.WaitAll(Task.Run(() => throw new InvalidOperationException()));
        }
        catch (InvalidOperationException) {
            Console.WriteLine("Invalid operation caught");
        }
        catch (AggregateException) {
            Console.WriteLine("Aggregate exception caught");
        }
        catch (Exception) {
            Console.WriteLine("General exception caught");
        }
    }
}

A Invalid operation caught

B Aggregate exception caught

C General exception caught

D No output, program crashes

💡 Hint

Task.WaitAll wraps exceptions in AggregateException.

Task.WaitAll throws AggregateException which is caught by the matching catch block printing "Aggregate exception caught".

🧠 Conceptual

expert

Order of multiple catch blocks and exception handling

Which statement about multiple catch blocks in C# is correct?

A Catch blocks must be ordered from most specific to most general exception types to compile.

B Catch blocks must be ordered from most general to most specific exception types.

C Catch blocks can be in any order; the first matching block executes at runtime.

D Only one catch block is allowed per try block in C#.

💡 Hint

Think about how C# compiler checks catch block order.

C# requires catch blocks to be ordered from most specific to most general exception types to avoid unreachable code errors.

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