This keyword behavior in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the current object's name using this keyword.

C Sharp (C#)

public class Person {
    public string Name;
    public void PrintName() {
        Console.WriteLine(this.[1]);
    }
}

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

Athis

BName

Cname

DPrintName

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'name' instead of 'Name' which is case-sensitive.

Trying to use 'this' alone without a member name.

The this keyword refers to the current object instance. To access the Name field, use this.Name.

2fill in blank

medium

Complete the constructor to assign the parameter to the instance variable using this keyword.

C Sharp (C#)

public class Car {
    public string Model;
    public Car(string model) {
        this.[1] = model;
    }
}

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

Amodel

BCar

Cthis

DModel

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning to the parameter instead of the instance variable.

Using lowercase 'model' on the left side which refers to the parameter.

The instance variable is Model. Use this.Model to refer to it and assign the parameter model.

3fill in blank

hard

Fix the error by completing the method to return the current object's description using this keyword.

C Sharp (C#)

public class Book {
    public string Title;
    public string GetDescription() {
        return this.[1];
    }
}

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

ATitle

Btitle

CGetDescription

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'title' which does not match the field name.

Returning this alone which is not a string.

The field is named Title with uppercase T. Use this.Title to access it correctly.

4fill in blank

hard

Fill both blanks to create a method that compares the current object's age with another object's age using this keyword.

C Sharp (C#)

public class Animal {
    public int Age;
    public bool IsOlderThan(Animal other) {
        return this.[1] [2] other.Age;
    }
}

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

AAge

B>

C<

Dother

Attempts:

3 left

💡 Hint

Common Mistakes

Using other on the left side instead of this.

Using the wrong comparison operator.

Use this.Age to get the current object's age and compare it with other.Age using the greater than operator >.

5fill in blank

hard

Fill all three blanks to create a method that updates the current object's score only if the new score is higher, using this keyword.

C Sharp (C#)

public class Player {
    public int Score;
    public void UpdateScore(int newScore) {
        if (newScore [1] this.[2]) {
            this.[3] = newScore;
        }
    }
}

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

A<

BScore

C>

DnewScore

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator like '<' instead of '>'.

Assigning to newScore instead of this.Score.

The method checks if newScore is greater than this.Score. If yes, it updates this.Score to newScore.

Practice

1. What does the this keyword refer to inside a class in C#?

easy

A. A local variable inside a method

B. A static method of the class

C. The base class of the current class

D. The current instance of the class

Solution

1. Step 1: Understand the role of this

   The this keyword always points to the current object instance inside its class.

2. Step 2: Differentiate from other options

   It does not refer to static methods, local variables, or base classes.

3. Final Answer:

   The current instance of the class -> Option D

4. Quick Check:

   this = current object [OK]

Hint: Remember: this means current object instance [OK]

Common Mistakes:

• Confusing this with static members
• Thinking this refers to base class
• Assuming this is a local variable

2. Which of the following is the correct way to use this to refer to a class field when a method parameter has the same name?

easy

A. public void SetName(string name) { this.name = name; }

B. public void SetName(string name) { name = name; }

C. public void SetName(string name) { name = this.name; }

D. public void SetName(string name) { SetName = name; }

Solution

1. Step 1: Identify the naming conflict

   The parameter name hides the class field name.

2. Step 2: Use this to refer to the field

   this.name = name; assigns the parameter value to the class field.

3. Final Answer:

   public void SetName(string name) { this.name = name; } -> Option A

4. Quick Check:

   Use this to access fields with same name [OK]

Hint: Use this.field to avoid name conflicts [OK]

Common Mistakes:

• Assigning parameter to itself
• Reversing assignment order
• Using invalid syntax for assignment

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

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

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

medium

A. Name

B. Compilation error

C. Alice

D. null

Solution

1. Step 1: Analyze constructor assignment

   The constructor assigns the parameter Name to the field Name using this.Name = Name;.

2. Step 2: Check output of PrintName()

   The method prints the field Name, which holds "Alice".

3. Final Answer:

   Alice -> Option C

4. Quick Check:

   Constructor sets field, print shows "Alice" [OK]

Hint: Constructor sets field with this, print shows value [OK]

Common Mistakes:

• Confusing parameter and field values
• Expecting default null output
• Thinking this causes error

4. Identify the error in this code snippet:

class Car {
  public string Model;
  public Car(string Model) {
    Model = Model;
  }
}

medium

A. Missing this keyword causes field not to be set

B. Constructor syntax is invalid

C. Field Model should be static

D. Parameter name cannot be same as field name

Solution

1. Step 1: Understand assignment in constructor

   The assignment Model = Model; assigns the parameter to itself, not the field.

2. Step 2: Use this to fix

   Using this.Model = Model; assigns the parameter value to the field.

3. Final Answer:

   Missing this keyword causes field not to be set -> Option A

4. Quick Check:

   Use this to assign fields when names overlap [OK]

Hint: Assign fields with this.field = param to avoid errors [OK]

Common Mistakes:

• Assuming parameter assigns field automatically
• Thinking constructor syntax is wrong
• Believing parameter names must differ from fields

5. Consider this class with two constructors:

class Box {
  public int Width, Height;
  public Box() : this(10, 20) {}
  public Box(int Width, int Height) {
    this.Width = Width;
    this.Height = Height;
  }
}

var b = new Box();
Console.WriteLine($"{b.Width}, {b.Height}");

What will be the output and why?

hard

A. 0, 0 because fields are not initialized

B. 10, 20 because the parameterless constructor calls the other constructor using this

C. Compilation error due to constructor chaining

D. Runtime error because of infinite constructor call

Solution

1. Step 1: Understand constructor chaining with this

   The parameterless constructor calls the two-parameter constructor with values 10 and 20.

2. Step 2: Check field initialization

   The two-parameter constructor sets Width and Height to 10 and 20 respectively.

3. Final Answer:

   10, 20 because the parameterless constructor calls the other constructor using this -> Option B

4. Quick Check:

   Constructor chaining with this sets fields [OK]

Hint: Use this(args) to call another constructor [OK]

Common Mistakes:

• Thinking fields remain default zero
• Assuming constructor chaining causes errors
• Confusing this with base constructor calls