Constructors and initialization in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constructor for the class.

C Sharp (C#)

public class Person {
    public string Name;
    [1] Person(string name) {
        Name = name;
    }
}

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

Apublic

Bvoid

Cstatic

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' as constructor return type

Using 'static' keyword for constructor

Omitting access modifier

The constructor must have the public access modifier to be accessible and properly defined.

2fill in blank

medium

Complete the constructor to initialize the Age field.

C Sharp (C#)

public class Person {
    public int Age;
    public Person(int age) {
        [1] = age;
    }
}

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

Athis.Age

Bage

CPerson.Age

DAge

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning parameter to itself

Using class name instead of this

Omitting this and causing ambiguity

Use this.Age to refer to the instance field and assign the parameter value.

3fill in blank

hard

Fix the error in the constructor to properly initialize the field.

C Sharp (C#)

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

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

Athis.Model

BModel

Cmodel

DCar.Model

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning field to itself

Using class name to access instance field

Using 'this' on the right side instead of parameter

The parameter model should be assigned to the field Model.

4fill in blank

hard

Fill both blanks to create a constructor that initializes both fields.

C Sharp (C#)

public class Book {
    public string Title;
    public int Pages;
    public Book([1] title, [2] pages) {
        Title = title;
        Pages = pages;
    }
}

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

Apublic

Bprivate

Cint

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong access modifier

Omitting parameter types

Using field types as parameter names

Constructor parameters need types and the constructor should be public.

5fill in blank

hard

Fill all three blanks to create a constructor that initializes fields with different names.

C Sharp (C#)

public class Student {
    public string Name;
    public int Grade;
    [1] Student([2] studentName, int studentGrade) {
        Name = [3];
        Grade = studentGrade;
    }
}

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

Apublic

BstudentName

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names

Omitting types

Assigning wrong variables

The constructor is public, parameters need types, and the field Name is assigned the parameter studentName.

Practice

1. What is the main purpose of a constructor in a C# class?

easy

A. To define methods that return values

B. To declare variables inside a class

C. To initialize new objects with starting values

D. To inherit properties from another class

Solution

1. Step 1: Understand what constructors do

   Constructors are special methods that run when an object is created to set initial values.

2. Step 2: Compare options with constructor purpose

   Only To initialize new objects with starting values describes initializing new objects, which matches the constructor's role.

3. Final Answer:

   To initialize new objects with starting values -> Option C

4. Quick Check:

   Constructor purpose = initialize objects [OK]

Hint: Constructors set initial values when creating objects [OK]

Common Mistakes:

• Confusing constructors with regular methods
• Thinking constructors return values
• Mixing constructors with inheritance

2. Which of the following is the correct syntax for a constructor in C# for a class named Car?

easy

A. public Car() { }

B. void Car() { }

C. public void Car() { }

D. public Car(void) { }

Solution

1. Step 1: Recall constructor syntax rules

   Constructors have the same name as the class and no return type, but must have an access modifier like public.

2. Step 2: Check each option

   public Car() { } matches: public + class name + parentheses + no return type. Others have void return or wrong syntax.

3. Final Answer:

   public Car() { } -> Option A

4. Quick Check:

   Constructor syntax = public ClassName() [OK]

Hint: Constructor name = class name, no return type [OK]

Common Mistakes:

• Adding a return type like void
• Using incorrect parameter syntax
• Omitting access modifier

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

class Person {
  public string Name;
  public Person(string name) {
    Name = name;
  }
}

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

medium

A. Compilation error

B. Anna

C. null

D. Name

Solution

1. Step 1: Understand constructor usage

   The constructor sets the Name field to the passed string "Anna" when creating the Person object.

2. Step 2: Check output of Console.WriteLine

   Since p.Name was set to "Anna", printing p.Name outputs "Anna".

3. Final Answer:

   Anna -> Option B

4. Quick Check:

   Constructor sets Name = "Anna" so output = Anna [OK]

Hint: Constructor sets fields; output shows assigned value [OK]

Common Mistakes:

• Assuming default null value instead of assigned
• Confusing field name with value
• Expecting compilation error due to constructor

4. Identify the error in this C# class constructor and how to fix it:

class Book {
  public string Title;
  public Book(string title) {
    title = Title;
  }
}

medium

A. Title should be private, not public

B. Constructor name should be lowercase book

C. Missing return type void in constructor

D. The assignment is reversed; should be Title = title;

Solution

1. Step 1: Analyze the assignment inside constructor

   The code assigns title = Title, which sets the parameter to the field's value, not the other way around.

2. Step 2: Correct the assignment direction

   It should assign the field Title to the parameter value: Title = title; to initialize properly.

3. Final Answer:

   The assignment is reversed; should be Title = title; -> Option D

4. Quick Check:

   Field = parameter to initialize correctly [OK]

Hint: Assign field = parameter inside constructor [OK]

Common Mistakes:

• Reversing assignment direction
• Changing constructor name incorrectly
• Adding return type to constructor

5. Given this class with two constructors:

class Rectangle {
  public int Width, Height;
  public Rectangle() {
    Width = 1;
    Height = 1;
  }
  public Rectangle(int size) {
    Width = size;
    Height = size;
  }
}

var r1 = new Rectangle();
var r2 = new Rectangle(5);
Console.WriteLine(r1.Width + "," + r1.Height);
Console.WriteLine(r2.Width + "," + r2.Height);

What is the output?

hard

A. 1,1
5,5

B. 0,0
5,5

C. 1,1
1,1

D. Compilation error due to constructor overload

Solution

1. Step 1: Understand constructor overloading

   The class has two constructors: one with no parameters sets Width and Height to 1; the other sets both to the given size.

2. Step 2: Trace object creation and output

   r1 uses the no-parameter constructor, so Width=1, Height=1. r2 uses the int parameter constructor with 5, so Width=5, Height=5.

3. Final Answer:

   1,1 5,5 -> Option A

4. Quick Check:

   Overloaded constructors set different sizes correctly [OK]

Hint: Overloaded constructors run based on arguments [OK]

Common Mistakes:

• Assuming default values are zero
• Thinking constructor overload causes error
• Mixing up which constructor runs