Custom exception classes in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of throwing and catching a custom exception

What will be the output of this C# program when it throws and catches a custom exception?

C Sharp (C#)

using System;

class MyCustomException : Exception {
    public MyCustomException(string message) : base(message) {}
}

class Program {
    static void Main() {
        try {
            throw new MyCustomException("Oops, something went wrong!");
        } catch (MyCustomException ex) {
            Console.WriteLine(ex.Message);
        }
    }
}

A MyCustomException

B No output, program crashes

C System.Exception: Oops, something went wrong!

D Oops, something went wrong!

💡 Hint

Look at what ex.Message prints when caught.

The custom exception inherits from Exception and passes the message to the base class. Catching it and printing ex.Message outputs the message string.

🧠 Conceptual

intermediate

Purpose of custom exception classes

Why do programmers create custom exception classes instead of using only built-in exceptions?

A To provide more specific error information related to their application domain

B To automatically fix errors without user intervention

C Because built-in exceptions cannot be caught in try-catch blocks

D To make the program run faster by avoiding built-in exceptions

💡 Hint

Think about how custom exceptions help in understanding errors better.

Custom exceptions allow programmers to signal specific problems related to their application, making error handling clearer and more precise.

🔧 Debug

advanced

Identify the error in this custom exception class

What error will this code produce when compiled?

C Sharp (C#)

using System;

class MyException : Exception {
    public MyException(string message) {
        base.Message = message;
    }
}

class Program {
    static void Main() {
        throw new MyException("Error occurred");
    }
}

A Compile-time error: Cannot assign to 'Message' because it is read-only

B Runtime error: NullReferenceException

C No error, prints 'Error occurred'

D Compile-time error: Missing base constructor call

💡 Hint

Check if Message property can be assigned directly.

The Message property in Exception is read-only. You must pass the message to the base constructor instead of assigning it.

📝 Syntax

advanced

Correct syntax to define a custom exception with serialization support

Which option correctly defines a custom exception class that supports serialization?

A

using System;
using System.Runtime.Serialization;

class MyException : Exception {
    public MyException() {}
    public MyException(string message) : base(message) {}
    protected MyException(SerializationInfo info, StreamingContext context) : base(info, context) {}
}

B

using System;

class MyException : Exception {
    public MyException() {}
    public MyException(string message) : base(message) {}
    protected MyException(SerializationInfo info, StreamingContext context) {}
}

C

using System;
using System.Runtime.Serialization;

[Serializable]
class MyException : Exception {
    public MyException() {}
    public MyException(string message) : base(message) {}
    protected MyException(SerializationInfo info, StreamingContext context) : base(info, context) {}
}

D

using System;
using System.Runtime.Serialization;

[Serializable]
class MyException {
    public MyException() {}
    public MyException(string message) {}
}

💡 Hint

Serialization requires the [Serializable] attribute and a protected constructor calling base.

Option C correctly adds the [Serializable] attribute and implements the protected constructor calling the base constructor with SerializationInfo and StreamingContext.

🚀 Application

expert

Determine the number of caught exceptions

Given this code, how many exceptions will be caught and printed?

C Sharp (C#)

using System;

class CustomEx : Exception {}

class Program {
    static void Main() {
        int count = 0;
        try {
            throw new CustomEx();
        } catch (Exception) {
            count++;
            try {
                throw new CustomEx();
            } catch (CustomEx) {
                count++;
            }
        }
        Console.WriteLine(count);
    }
}

A 1

B 2

C 0

D 3

💡 Hint

Count increments each time an exception is caught.

The first throw is caught by catch(Exception), incrementing count to 1. Then inside that catch, another throw is caught by catch(CustomEx), incrementing count to 2. So total printed is 2.