Class declaration syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple class instance property

What is the output of this C# code?

C Sharp (C#)

class Person {
    public string Name = "Alice";
}

var p = new Person();
Console.WriteLine(p.Name);

A null

B Name

C Alice

D Person

💡 Hint

Look at the value assigned to the Name field inside the Person class.

The class Person has a public field Name initialized to "Alice". Creating an instance and printing p.Name outputs "Alice".

📝 Syntax

intermediate

Identify the syntax error in class declaration

Which option contains a syntax error in the class declaration?

A class Plane { public void Fly() { Console.WriteLine("Flying"); } }

B class Bike { private string model; }

C public class Car { public int Speed; }

D public sealed class Boat { }

💡 Hint

Check if all braces are properly closed.

Option A is missing the closing brace for the class Plane, causing a syntax error.

🔧 Debug

advanced

Why does this class instantiation cause an error?

What error will this code produce and why?

C Sharp (C#)

class Animal {
    private Animal() { }
}

var a = new Animal();

A Compile-time error: Missing semicolon

B Compile-time error: 'Animal.Animal()' is inaccessible due to its protection level

C No error, outputs 'Animal created'

D Runtime error: NullReferenceException

💡 Hint

Check the accessibility of the constructor.

The constructor is private, so it cannot be called outside the class. Trying to create an instance causes a compile-time accessibility error.

🧠 Conceptual

advanced

Effect of 'sealed' keyword on class inheritance

What happens if you try to inherit from a sealed class in C#?

C Sharp (C#)

sealed class Vehicle { }
class Car : Vehicle { }

A Car inherits Vehicle successfully

B Runtime error: InvalidCastException

C Warning but compiles and runs

D Compile-time error: cannot derive from sealed type 'Vehicle'

💡 Hint

The sealed keyword prevents inheritance.

A sealed class cannot be used as a base class. Attempting to inherit from it causes a compile-time error.

🚀 Application

expert

Number of members in a class with properties and methods

How many members does this class have?

C Sharp (C#)

public class Calculator {
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
    public int Result { get; private set; }
    private void Reset() { Result = 0; }
}

A 4

B 3

C 5

D 6

💡 Hint

Count all methods and properties declared inside the class.

The class has 2 public methods (Add, Subtract), 1 property (Result), and 1 private method (Reset), totaling 4 members.