Custom exception classes in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a custom exception class named MyException.

C Sharp (C#)

public class MyException : [1] { }

Drag options to blanks, or click blank then click option'

AException

BError

CBaseException

DSystemException

Attempts:

3 left

💡 Hint

Common Mistakes

Using Error or BaseException which are not valid base classes in C#.

Forgetting to inherit from any class.

The custom exception class should inherit from Exception to behave like a standard exception.

2fill in blank

medium

Complete the constructor to call the base Exception constructor with a message.

C Sharp (C#)

public class MyException : Exception {
    public MyException(string message) : [1](message) { }
}

Drag options to blanks, or click blank then click option'

Athis

Bsuper

Cbase

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using this instead of base, which calls the current class constructor.

Using super or parent which are not C# keywords.

Use base to call the constructor of the parent Exception class with the message.

3fill in blank

hard

Fix the error in the custom exception class by adding the missing constructor for serialization.

C Sharp (C#)

using System;
using System.Runtime.Serialization;

[Serializable]
public class MyException : Exception {
    public MyException(string message) : base(message) { }
    protected MyException(SerializationInfo info, [1] context) : base(info, context) { }
}

Drag options to blanks, or click blank then click option'

ASerializationContext

BContext

CStreamContext

DStreamingContext

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter types like SerializationContext or Context.

Omitting the protected constructor needed for serialization.

The protected constructor for serialization requires a StreamingContext parameter.

4fill in blank

hard

Fill both blanks to complete the custom exception class with a default constructor and a message constructor.

C Sharp (C#)

public class MyException : Exception {
    public MyException() : [1]() { }
    public MyException(string message) : [2](message) { }
}

Drag options to blanks, or click blank then click option'

Abase

Bthis

Csuper

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using this instead of base, which calls another constructor in the same class.

Using super or parent which are not valid in C#.

Both constructors should call the base Exception constructors using base.

5fill in blank

hard

Fill all three blanks to complete the custom exception class with default, message, and serialization constructors.

C Sharp (C#)

using System;
using System.Runtime.Serialization;

[Serializable]
public class MyException : Exception {
    public MyException() : [1]() { }
    public MyException(string message) : [2](message) { }
    protected MyException(SerializationInfo info, [3] context) : base(info, context) { }
}

Drag options to blanks, or click blank then click option'

Abase

Bthis

CStreamingContext

DSerializationContext

Attempts:

3 left

💡 Hint

Common Mistakes

Using this instead of base for constructors.

Using wrong parameter type for serialization constructor.

The default and message constructors call base, and the serialization constructor uses StreamingContext as the parameter type.

Practice

1. What is the main reason to create a custom exception class in C#?

easy

A. To automatically fix errors when they occur

B. To make the program run faster

C. To avoid using try-catch blocks

D. To represent specific error conditions clearly in your program

Solution

1. Step 1: Understand the purpose of exceptions

   Exceptions represent errors or unexpected situations in a program.

2. Step 2: Identify why custom exceptions are used

   Custom exceptions help describe specific problems clearly, making error handling easier and more meaningful.

3. Final Answer:

   To represent specific error conditions clearly in your program -> Option D

4. Quick Check:

   Custom exceptions clarify errors = A [OK]

Hint: Custom exceptions explain specific errors clearly [OK]

Common Mistakes:

• Thinking custom exceptions improve speed
• Believing they remove need for try-catch
• Assuming they fix errors automatically

2. Which of the following is the correct way to declare a custom exception class named MyException in C#?

easy

A. class MyException : Exception { public MyException(string message) : base(message) {} }

B. class MyException { public MyException(string message) {} }

C. class MyException : int { public MyException(string message) : base(message) {} }

D. class MyException : Exception { public void MyException(string message) {} }

Solution

1. Step 1: Check inheritance from Exception

   Custom exceptions must inherit from Exception to behave like exceptions.

2. Step 2: Verify constructor calls base constructor

   The constructor should call base(message) to pass the error message properly.

3. Final Answer:

   class MyException : Exception { public MyException(string message) : base(message) {} } -> Option A

4. Quick Check:

   Inherit Exception + call base constructor = A [OK]

Hint: Inherit Exception and call base constructor for message [OK]

Common Mistakes:

• Not inheriting from Exception
• Using wrong base class like int
• Defining constructor as void method

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

class MyException : Exception { public MyException(string message) : base(message) {} }
try {
  throw new MyException("Error happened");
} catch (MyException ex) {
  Console.WriteLine(ex.Message);
}

medium

A. Exception caught

B. Error happened

C. MyException

D. No output

Solution

1. Step 1: Understand the throw statement

   The code throws a MyException with message "Error happened".

2. Step 2: Catch block prints exception message

   The catch block catches MyException and prints ex.Message, which is "Error happened".

3. Final Answer:

   Error happened -> Option B

4. Quick Check:

   Throw and catch prints message = C [OK]

Hint: Catch prints exception message property [OK]

Common Mistakes:

• Expecting class name instead of message
• Thinking catch block won't run
• Assuming no output from exception

4. Identify the error in this custom exception class declaration:

class MyError : Exception {
  public MyError(string msg) {
    base(msg);
  }
}

medium

A. The class must not inherit from Exception

B. The constructor should be named differently from the class

C. The constructor should call base(msg) using a colon, not inside the body

D. The base class Exception does not accept a string parameter

Solution

1. Step 1: Check constructor syntax for base call

   In C#, calling the base class constructor must be done with a colon after the constructor signature, not inside the body.

2. Step 2: Identify correct syntax

   The correct syntax is public MyError(string msg) : base(msg) {}, not calling base(msg); inside the constructor body.

3. Final Answer:

   The constructor should call base(msg) using a colon, not inside the body -> Option C

4. Quick Check:

   Base constructor call uses colon syntax = B [OK]

Hint: Call base constructor with colon, not inside method body [OK]

Common Mistakes:

• Calling base constructor inside body instead of colon
• Not inheriting from Exception
• Misnaming constructor

5. You want to create a custom exception InvalidAgeException that should be thrown when a user's age is less than 0 or greater than 120. Which of the following code snippets correctly defines and uses this exception?

hard

A. class InvalidAgeException : Exception { public InvalidAgeException(string msg) : base(msg) {} }void CheckAge(int age) { if(age < 0 || age > 120) throw new InvalidAgeException("Age is invalid"); }

B. class InvalidAgeException { public InvalidAgeException(string msg) {} }void CheckAge(int age) { if(age < 0 || age > 120) throw new InvalidAgeException("Age is invalid"); }

C. class InvalidAgeException : Exception { public void InvalidAgeException(string msg) {} }void CheckAge(int age) { if(age < 0 || age > 120) throw new InvalidAgeException("Age is invalid"); }

D. class InvalidAgeException : Exception { public InvalidAgeException() {} }void CheckAge(int age) { if(age < 0 || age > 120) throw new InvalidAgeException(); }

Solution

1. Step 1: Verify custom exception class definition

   The class inherits from Exception and has a constructor calling base(msg) to pass the message.

2. Step 2: Check usage in method

   The method throws the exception with a message when age is invalid, which matches the requirement.

3. Final Answer:

   Correct class inheritance, constructor, and usage with message -> Option A

4. Quick Check:

   Inherit Exception + throw with message = D [OK]

Hint: Inherit Exception, add constructor, throw with message [OK]

Common Mistakes:

• Not inheriting from Exception
• Defining constructor as void method
• Missing message in exception constructor