Why classes are needed in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a class named Car.

C Sharp (C#)

public [1] Car {
    // class body
}

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

Amethod

Bclass

Cvariable

Dinterface

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'method' or 'variable' instead of 'class' to declare a class.

Confusing 'interface' with 'class' keyword.

The keyword class is used to declare a class in C#.

2fill in blank

medium

Complete the code to create an object of the Car class.

C Sharp (C#)

Car myCar = new [1]();

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

AVehicle

BClass

CObject

DCar

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different class name than the one declared.

Using 'Object' or 'Class' instead of the class name.

To create an object, use the class name with the new keyword.

3fill in blank

hard

Fix the error in the code to access the Car's speed property.

C Sharp (C#)

int speed = myCar.[1];

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

ASpeed()

Bspeed()

CSpeed

Dspeed

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses when accessing a property.

Using incorrect capitalization.

Properties are accessed without parentheses and with correct capitalization.

4fill in blank

hard

Fill both blanks to define a method named Drive inside the Car class.

C Sharp (C#)

public [1] [2]() {
    Console.WriteLine("Driving");
}

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

Avoid

Bint

CDrive

DCar

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name as the method name.

Using a return type other than void when no value is returned.

The method return type is void and the method name is Drive.

5fill in blank

hard

Fill all three blanks to create a Car object, set its speed, and print it.

C Sharp (C#)

Car [1] = new Car();
[1].[2] = 60;
Console.WriteLine([1].[2]);

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

AmyCar

Bspeed

CSpeed

DcarSpeed

Attempts:

3 left

💡 Hint

Common Mistakes

Using different object names in different lines.

Using incorrect property names or capitalization.

Use the same object name myCar and the correct property name Speed to set and print the speed.

Practice

1. Why do we use classes in C# programming?

easy

A. To make the program run slower

B. To write code faster without any structure

C. To avoid using variables

D. To group related data and actions together

Solution

1. Step 1: Understand the purpose of classes

   Classes help organize data (variables) and actions (methods) that belong together.

2. Step 2: Compare options with class purpose

   Only grouping related data and actions matches the main reason for classes.

3. Final Answer:

   To group related data and actions together -> Option D

4. Quick Check:

   Classes group data and actions [OK]

Hint: Classes bundle data and behavior in one place [OK]

Common Mistakes:

• Thinking classes slow down programs
• Believing classes are only for speed
• Confusing classes with variables

2. Which of the following is the correct way to declare a simple class named Car in C#?

easy

A. class Car { }

B. Car class { }

C. class = Car { }

D. class Car() { }

Solution

1. Step 1: Recall C# class declaration syntax

   In C#, a class is declared using the keyword class followed by the class name and curly braces.

2. Step 2: Check each option

   class Car { } matches the correct syntax: class Car { }. Others have syntax errors.

3. Final Answer:

   class Car { } -> Option A

4. Quick Check:

   Correct class syntax [OK]

Hint: Use 'class ClassName { }' to declare classes [OK]

Common Mistakes:

• Putting parentheses after class name
• Swapping 'class' and class name
• Using '=' sign in declaration

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

class Dog {
  public string Name = "Buddy";
}

class Program {
  static void Main() {
    Dog myDog = new Dog();
    Console.WriteLine(myDog.Name);
  }
}

medium

A. Buddy

B. myDog

C. Dog

D. Name

Solution

1. Step 1: Understand object creation and field access

   The code creates a new Dog object and accesses its Name field which is set to "Buddy".

2. Step 2: Determine what is printed

   The Console.WriteLine prints the value of myDog.Name, which is "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Object field value printed = Buddy [OK]

Hint: Object.field prints the stored value [OK]

Common Mistakes:

• Printing the object name instead of field
• Confusing class name with field value
• Expecting variable name as output

4. Identify the error in this class definition:

class Person {
  string name;
  void SetName(string newName) {
    name = newName;
  }
}

class Program {
  static void Main() {
    Person p = new Person();
    p.SetName("Alice");
  }
}

medium

A. Class Person must inherit from another class

B. Field name should be static

C. Method SetName must be public to be accessible

D. Cannot create object of class Person

Solution

1. Step 1: Check method accessibility

   The method SetName has no access modifier, so it is private by default and not accessible outside the class.

2. Step 2: Understand object method call

   In Main, p.SetName("Alice") tries to call a private method, causing an error.

3. Final Answer:

   Method SetName must be public to be accessible -> Option C

4. Quick Check:

   Private method can't be called outside class [OK]

Hint: Make methods public to call them from outside [OK]

Common Mistakes:

• Assuming methods are public by default
• Thinking fields must be static
• Believing inheritance is mandatory

5. You want to model a Book with a title and author, and a method to display its info. Why is using a class better than separate variables?

hard

A. Separate variables run faster and use less memory

B. Classes keep related data and behavior together, making code reusable and clear

C. Classes make code longer and harder to read

D. Using separate variables avoids the need for methods

Solution

1. Step 1: Understand the benefit of grouping data and methods

   A class groups the book's title, author, and display method, making the code organized and reusable.

2. Step 2: Compare with separate variables

   Separate variables scatter data and methods, making code harder to maintain and reuse.

3. Final Answer:

   Classes keep related data and behavior together, making code reusable and clear -> Option B

4. Quick Check:

   Classes improve organization and reuse [OK]

Hint: Group data and actions in classes for clarity [OK]

Common Mistakes:

• Thinking classes slow down programs
• Believing separate variables are always better
• Ignoring benefits of code reuse