Class declaration syntax in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple class named Car.

C Sharp (C#)

public [1] Car {
    // class body
}

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

Ainterface

Bstruct

Cclass

Denum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'struct' instead of 'class' for class declaration.

Using 'interface' or 'enum' which are different types.

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

2fill in blank

medium

Complete the code to declare a public class named Person.

C Sharp (C#)

[1] class Person {
    // properties and methods
}

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

Apublic

Bprotected

Cprivate

Dinternal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'private' which restricts access.

Using 'protected' which is for inheritance only.

The keyword public makes the class accessible from other parts of the program.

3fill in blank

hard

Fix the error in the class declaration to make it valid.

C Sharp (C#)

public class [1] {
    // class body
}

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

ACar123

B123Car

CCar-Model

DCar Model

Attempts:

3 left

💡 Hint

Common Mistakes

Starting class name with a number.

Including spaces or hyphens in the class name.

Class names must start with a letter and cannot contain spaces or hyphens. Car123 is valid.

4fill in blank

hard

Fill both blanks to declare a sealed class named Logger.

C Sharp (C#)

[1] sealed [2] Logger {
    // class body
}

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

Apublic

Bclass

Cstruct

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'struct' instead of 'class'.

Using 'private' when 'public' is needed.

The correct syntax is public sealed class Logger. public is the access modifier and class declares the type.

5fill in blank

hard

Fill all three blanks to declare an abstract class named Shape with public access.

C Sharp (C#)

[1] [2] [3] Shape {
    // class body
}

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

Aprotected

Babstract

Cclass

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'protected' instead of 'public'.

Omitting the 'abstract' keyword.

Using 'struct' instead of 'class'.

The correct declaration is public abstract class Shape. public is the access modifier, abstract means the class cannot be instantiated, and class declares the type.

Practice

1. What is the correct way to declare a class named Car in C#?

easy

A. Car class { }

B. class Car { }

C. class = Car { }

D. class: Car { }

Solution

1. Step 1: Understand class declaration syntax

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

2. Step 2: Match the correct syntax

   class Car { } uses class Car { }, which is the correct syntax for declaring a class named Car.

3. Final Answer:

   class Car { } -> Option B

4. Quick Check:

   Class declaration = class ClassName { } [OK]

Hint: Remember: class keyword + name + braces [OK]

Common Mistakes:

• Putting class name before keyword
• Using = or : instead of space
• Missing curly braces

2. Which of the following is a syntax error when declaring a class in C#?

easy

A. public class Person { }

B. class Animal { }

C. class 123Car { }

D. internal class House { }

Solution

1. Step 1: Check class name rules

   Class names must start with a letter or underscore, not a number.

2. Step 2: Identify invalid class name

   class 123Car { } uses class 123Car { }, which starts with digits, causing a syntax error.

3. Final Answer:

   class 123Car { } -> Option C

4. Quick Check:

   Class names cannot start with numbers [OK]

Hint: Class names must start with letter or underscore [OK]

Common Mistakes:

• Starting class name with a digit
• Using spaces in class name
• Using reserved keywords as class names

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

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

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

medium

A. Buddy

B. Name

C. Dog

D. Compilation error

Solution

1. Step 1: Understand class field initialization

   The class Dog has a public field Name initialized to "Buddy".

2. Step 2: Trace the program output

   In Main, a Dog object is created and d.Name is printed, so output is "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Field value printed = Buddy [OK]

Hint: Prints field value assigned in class [OK]

Common Mistakes:

• Confusing class name with field value
• Expecting method output instead of field
• Assuming compilation error without reason

4. Identify the error in this class declaration:

class Book
{
  string title;
  void SetTitle(string t)
  {
    title = t;
  }
}

medium

A. Missing access modifiers for field and method

B. Class name should be lowercase

C. Method SetTitle must return a value

D. Field title must be static

Solution

1. Step 1: Check access modifiers in class members

   By default, class members are private, but it's good practice to specify access modifiers explicitly.

2. Step 2: Identify missing access modifiers

   Field title and method SetTitle lack access modifiers like private or public, which can cause confusion or errors in some contexts.

3. Final Answer:

   Missing access modifiers for field and method -> Option A

4. Quick Check:

   Always specify access modifiers [OK]

Hint: Always add public/private to fields and methods [OK]

Common Mistakes:

• Assuming lowercase class names are required
• Thinking void methods must return a value
• Believing fields must be static

5. You want to create a class Student with a field name and a method GetName that returns the student's name. Which is the correct complete class declaration?

hard

A. class Student { public string name; public void GetName() { return name; } }

B. class Student { string name; string GetName() { name; } }

C. class Student { public string name; string GetName() { return name; } }

D. class Student { public string name; public string GetName() { return name; } }

Solution

1. Step 1: Check field and method access modifiers

   The field name and method GetName should be public to be accessible outside the class.

2. Step 2: Verify method return type and body

   GetName returns a string, so its return type must be string and it must return name.

3. Step 3: Identify correct option

   class Student { public string name; public string GetName() { return name; } } correctly declares name as public string and GetName as public string method returning name.

4. Final Answer:

   class Student { public string name; public string GetName() { return name; } } -> Option D

5. Quick Check:

   Public field + public string method returning field [OK]

Hint: Method return type must match returned value type [OK]

Common Mistakes:

• Missing return statement in method
• Wrong method return type (void instead of string)
• Missing public keyword for accessibility