This keyword behavior in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of 'this' in instance method

What is the output of this C# program?

C Sharp (C#)

class Person {
    public string Name;
    public Person(string name) {
        this.Name = name;
    }
    public void PrintName() {
        System.Console.WriteLine(this.Name);
    }
}

var p = new Person("Alice");
p.PrintName();

A Alice

B Name

C System.Object

D Compilation error

💡 Hint

Remember 'this' refers to the current object instance.

The this keyword inside an instance method refers to the current object. Here, this.Name accesses the Name field of the Person instance, which was set to "Alice".

❓ Predict Output

intermediate

Using 'this' in static method

What happens when you try to compile and run this C# code?

C Sharp (C#)

class Sample {
    public static void Show() {
        System.Console.WriteLine(this.ToString());
    }
}

Sample.Show();

A Runtime error: NullReferenceException

B Prints the class name 'Sample'

C Compilation error: 'this' is not available in static context

D Prints 'System.Object'

💡 Hint

Static methods do not have an instance context.

The this keyword cannot be used inside static methods because there is no instance of the class to refer to. This causes a compilation error.

❓ Predict Output

advanced

Output of 'this' in struct method

What is the output of this C# program?

C Sharp (C#)

struct Point {
    public int X, Y;
    public Point(int x, int y) {
        this.X = x;
        this.Y = y;
    }
    public void Move(int dx, int dy) {
        this.X += dx;
        this.Y += dy;
        System.Console.WriteLine($"{this.X},{this.Y}");
    }
}

var p = new Point(1, 2);
p.Move(3, 4);

A Runtime error

B 4,6

C Compilation error: Cannot use 'this' in struct

D 1,2

💡 Hint

Structs are value types but can use 'this' inside instance methods.

In a struct, this refers to the current value. The Move method updates the fields and prints the new coordinates.

❓ Predict Output

advanced

Output of 'this' in constructor chaining

What is the output of this C# program?

C Sharp (C#)

class Box {
    public int Size;
    public Box() : this(10) {
        System.Console.WriteLine(this.Size);
    }
    public Box(int size) {
        this.Size = size;
        System.Console.WriteLine(this.Size);
    }
}

var b = new Box();

A

10
10

B

0
10

C

10
0

D Compilation error

💡 Hint

Constructor chaining calls the parameterized constructor first.

The parameterized constructor sets Size to 10 and prints it. Then the parameterless constructor prints this.Size which is still 10.

🧠 Conceptual

expert

Behavior of 'this' in extension methods

In C#, what does the this keyword mean in the parameter of an extension method?

A It refers to the static class containing the extension method

B It refers to the base class of the extended class

C It is a syntax error to use 'this' in extension method parameters

D It refers to the instance of the class the method extends

💡 Hint

Extension methods add behavior to existing types by using 'this' in the first parameter.

In extension methods, this before the first parameter indicates the method extends that type, and inside the method, it refers to the instance of that type.