Exception hierarchy in .NET in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code snippet?

Consider the following C# code that catches exceptions:

try {
    throw new System.IO.FileNotFoundException("File missing");
} catch (System.Exception ex) {
    Console.WriteLine(ex.GetType().Name);
}

What will be printed?

C Sharp (C#)

try {
    throw new System.IO.FileNotFoundException("File missing");
} catch (System.Exception ex) {
    Console.WriteLine(ex.GetType().Name);
}

A FileNotFoundException

B SystemException

C Exception

D IOException

💡 Hint

FileNotFoundException inherits from IOException, which inherits from Exception.

The thrown exception is of type FileNotFoundException. The catch block catches it as Exception, but ex.GetType().Name returns the actual runtime type, which is FileNotFoundException.

❓ Predict Output

intermediate

What exception type is caught here?

Given this code snippet:

try {
    throw new System.ArgumentNullException("param");
} catch (System.SystemException ex) {
    Console.WriteLine(ex.GetType().Name);
}

What will be printed?

C Sharp (C#)

try {
    throw new System.ArgumentNullException("param");
} catch (System.SystemException ex) {
    Console.WriteLine(ex.GetType().Name);
}

A SystemException

B InvalidOperationException

C Exception

D ArgumentNullException

💡 Hint

ArgumentNullException inherits from SystemException.

The thrown exception is ArgumentNullException, which inherits from SystemException. The catch block catches SystemException, so it catches the thrown exception. The ex.GetType().Name returns the actual type ArgumentNullException.

❓ Predict Output

advanced

What error does this code raise?

Examine this code snippet:

try {
    throw new System.Exception("Error");
} catch (System.IO.IOException ex) {
    Console.WriteLine("IO error");
} catch (System.Exception ex) {
    Console.WriteLine("General error");
}

What will be printed?

C Sharp (C#)

try {
    throw new System.Exception("Error");
} catch (System.IO.IOException ex) {
    Console.WriteLine("IO error");
} catch (System.Exception ex) {
    Console.WriteLine("General error");
}

A General error

B IO error

C No output, program crashes

D Compilation error

💡 Hint

Exception is not an IOException, but it is an Exception.

The thrown exception is Exception. The first catch block for IOException does not match. The second catch block for Exception matches and prints General error.

❓ Predict Output

advanced

What is the output of this code with nested exceptions?

Look at this code:

try {
    try {
        throw new System.IndexOutOfRangeException("Index error");
    } catch (System.Exception ex) {
        throw new System.ApplicationException("App error", ex);
    }
} catch (System.ApplicationException ex) {
    Console.WriteLine(ex.InnerException.GetType().Name);
}

What will be printed?

C Sharp (C#)

try {
    try {
        throw new System.IndexOutOfRangeException("Index error");
    } catch (System.Exception ex) {
        throw new System.ApplicationException("App error", ex);
    }
} catch (System.ApplicationException ex) {
    Console.WriteLine(ex.InnerException.GetType().Name);
}

A Exception

B ApplicationException

C IndexOutOfRangeException

D NullReferenceException

💡 Hint

The inner exception is the original exception thrown inside the inner try block.

The inner try throws IndexOutOfRangeException. It is caught and wrapped inside an ApplicationException. The outer catch prints the type of the inner exception, which is IndexOutOfRangeException.

🧠 Conceptual

expert

Which exception type is the base for all CLR exceptions?

In the .NET exception hierarchy, which class is the ultimate base class for all exceptions thrown by the Common Language Runtime (CLR)?

A System.ApplicationException

B System.Exception

C System.SystemException

D System.Object

💡 Hint

Think about the root class that all exceptions inherit from.

System.Exception is the base class for all exceptions in .NET. System.SystemException and System.ApplicationException derive from it. System.Object is the base of all classes but not specifically for exceptions.

Practice

1. Which class is the base class for all exceptions in .NET?

easy

A. System.Error

B. System.Exception

C. System.ApplicationException

D. System.SystemException

Solution

1. Step 1: Understand the exception hierarchy

   All exceptions in .NET inherit from a common base class to unify error handling.

2. Step 2: Identify the root base class

   The root base class for all exceptions is System.Exception, from which other exceptions derive.

3. Final Answer:

   System.Exception -> Option B

4. Quick Check:

   Base exception class = System.Exception [OK]

Hint: Remember: All exceptions come from System.Exception [OK]

Common Mistakes:

• Confusing System.SystemException as the base
• Thinking System.ApplicationException is the root
• Assuming System.Error exists in .NET

2. Which of the following is the correct syntax to catch a specific exception type ArgumentNullException in C#?

easy

A. catch (ArgumentNullException e) { }

B. catch ArgumentNullException (e) { }

C. catch (Exception e) { }

D. catch ArgumentNullException { }

Solution

1. Step 1: Recall catch block syntax

   In C#, to catch a specific exception, use catch (ExceptionType variable) syntax.

2. Step 2: Match the correct syntax for ArgumentNullException

   The correct syntax is catch (ArgumentNullException e) { }, which declares the exception type and variable.

3. Final Answer:

   catch (ArgumentNullException e) { } -> Option A

4. Quick Check:

   Correct catch syntax = catch (ExceptionType e) [OK]

Hint: Use parentheses around exception type and variable in catch [OK]

Common Mistakes:

• Omitting parentheses around exception type
• Using wrong order like catch ExceptionType (e)
• Not declaring a variable for the exception

3. What will be the output of the following C# code?

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

medium

A. General error caught

B. Compilation error

C. No output, program crashes

D. Index error caught

Solution

1. Step 1: Identify the exception thrown

   Accessing index 5 in an array of size 2 throws IndexOutOfRangeException.

2. Step 2: Check which catch block handles it

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

3. Final Answer:

   Index error caught -> Option D

4. Quick Check:

   Specific catch runs before general [OK]

Hint: Specific exceptions catch before general ones [OK]

Common Mistakes:

• Thinking general Exception catch runs first
• Assuming program crashes without catch
• Confusing IndexOutOfRangeException with ArgumentException

4. Identify the error in this code snippet:

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

medium

A. Catch-all block must be last

B. Catch blocks order is incorrect

C. No error, code is correct

D. Missing exception variable in catch blocks

Solution

1. Step 1: Review catch block syntax

   Catch blocks can omit the exception variable if not used, which is valid here.

2. Step 2: Check catch block order

   The specific FormatException catch is before the general catch-all block, which is correct.

3. Final Answer:

   No error, code is correct -> Option C

4. Quick Check:

   Catch-all last and variable optional [OK]

Hint: Catch-all must be last; variable optional in catch [OK]

Common Mistakes:

• Thinking catch-all must have variable
• Placing catch-all before specific catch
• Assuming variable is mandatory in catch

5. You want to catch all exceptions except NullReferenceException and handle them differently. Which approach correctly implements this in C#?

hard

A. Use a catch block for Exception and rethrow if NullReferenceException

B. Use a single catch block for Exception and check exception type inside

C. Use two catch blocks: one for NullReferenceException, one for Exception

D. Use a catch block for NullReferenceException only

Solution

1. Step 1: Understand the requirement

   We want to handle all exceptions except NullReferenceException differently, so we must detect and exclude it.

2. Step 2: Evaluate approaches

   Use a catch block for Exception and rethrow if NullReferenceException uses a general catch for Exception, then rethrows if the exception is NullReferenceException, effectively excluding it from handling.

3. Final Answer:

   Use a catch block for Exception and rethrow if NullReferenceException -> Option A

4. Quick Check:

   Rethrow to exclude specific exceptions [OK]

Hint: Rethrow specific exceptions inside general catch [OK]

Common Mistakes:

• Catching NullReferenceException first but not rethrowing
• Handling all exceptions in one catch without rethrow
• Using only NullReferenceException catch block