Computed properties in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a computed property that returns the full name.

C Sharp (C#)

public class Person {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string FullName => [1];
}

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

AFirstName + " " + LastName

BFirstName - LastName

CFirstName / LastName

DFirstName * LastName

Attempts:

3 left

💡 Hint

Common Mistakes

Using arithmetic operators like - or * instead of + for strings.

Forgetting to add a space between names.

The computed property FullName combines FirstName and LastName with a space.

2fill in blank

medium

Complete the code to create a computed property that returns the area of a rectangle.

C Sharp (C#)

public class Rectangle {
    public double Width { get; set; }
    public double Height { get; set; }
    public double Area => [1];
}

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

AWidth - Height

BWidth / Height

CWidth * Height

DWidth + Height

Attempts:

3 left

💡 Hint

Common Mistakes

Adding width and height instead of multiplying.

Using division or subtraction by mistake.

The computed property Area multiplies Width and Height to get the rectangle's area.

3fill in blank

hard

Fix the error in the computed property that returns the initials of a person.

C Sharp (C#)

public class Person {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Initials => [1];
}

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

AFirstName[0].ToString() + " " + LastName[0].ToString()

BFirstName[0] + LastName[0]

CFirstName.Substring(0, 1) + LastName.Substring(0, 1)

DFirstName[0].ToString() + LastName[0].ToString()

Attempts:

3 left

💡 Hint

Common Mistakes

Adding chars directly without converting to string.

Forgetting to add a space between initials.

The computed property Initials returns the first letters of FirstName and LastName separated by a space. Using ToString() converts chars to strings for concatenation.

4fill in blank

hard

Fill both blanks to create a computed property that returns the perimeter of a rectangle.

C Sharp (C#)

public class Rectangle {
    public double Width { get; set; }
    public double Height { get; set; }
    public double Perimeter => 2 * ([1] + [2]);
}

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

AWidth

BHeight

CLength

DDepth

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties that don't exist like Length or Depth.

Forgetting to add both width and height inside the parentheses.

The perimeter of a rectangle is 2 times the sum of its width and height.

5fill in blank

hard

Fill all three blanks to create a computed property that returns the volume of a box.

C Sharp (C#)

public class Box {
    public double Width { get; set; }
    public double Height { get; set; }
    public double Depth { get; set; }
    public double Volume => [1] * [2] * [3];
}

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

AWidth

BHeight

CDepth

DLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property named Length which does not exist.

Missing one of the dimensions in the multiplication.

The volume of a box is the product of its width, height, and depth.

Practice

1. What is a computed property in C#?
public int Area => Width * Height;

easy

A. A property that calculates its value from other data automatically

B. A property that stores a fixed value in memory

C. A method that returns a value

D. A variable that can be changed anytime

Solution

1. Step 1: Understand the property syntax

   The property uses the lambda syntax with =>, which means it calculates the value when accessed.

2. Step 2: Recognize computed property behavior

   It does not store a value but returns Width * Height each time, so it is computed automatically.

3. Final Answer:

   A property that calculates its value from other data automatically -> Option A

4. Quick Check:

   Computed property = calculates value [OK]

Hint: Look for => syntax to spot computed properties [OK]

Common Mistakes:

• Thinking computed properties store values
• Confusing methods with properties
• Assuming computed properties can be set directly

2. Which of the following is the correct syntax for a read-only computed property in C#?

easy

A. public int Total() { return Price + Quantity; }

B. public int Total { get { return Price * Quantity; } }

C. public int Total => Price + Quantity { get; set; }

D. public int Total { set { Price = value; } }

Solution

1. Step 1: Identify read-only computed property syntax

   public int Total { get { return Price * Quantity; } } uses a property with only a get accessor returning a calculation, which is correct.

2. Step 2: Check other options for errors

   public int Total { set { Price = value; } } only has set, so not read-only. public int Total => Price + Quantity { get; set; } mixes expression body with get/set incorrectly. public int Total() { return Price + Quantity; } is a method, not a property.

3. Final Answer:

   public int Total { get { return Price * Quantity; } } -> Option B

4. Quick Check:

   Read-only computed property = get only [OK]

Hint: Read-only properties have only get accessor [OK]

Common Mistakes:

• Using set accessor in read-only properties
• Confusing methods with properties
• Incorrect expression body syntax

3. What is the output of this code?

class Box {
  public int Width { get; set; } = 3;
  public int Height { get; set; } = 4;
  public int Area => Width * Height;
}

var box = new Box();
Console.WriteLine(box.Area);

medium

A. 12

B. 7

C. 0

D. Error

Solution

1. Step 1: Identify property values

   Width is 3 and Height is 4 as set by default.

2. Step 2: Calculate computed property Area

   Area returns Width * Height = 3 * 4 = 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply Width and Height for Area [OK]

Common Mistakes:

• Adding instead of multiplying
• Assuming default values are zero
• Confusing property with method call

4. Find the error in this computed property code:

public class Circle {
  public double Radius { get; set; }
  public double Diameter => Radius * 2;
  public double Circumference { get { return 2 * Math.PI * Diameter; } set { Diameter = value; } }
}

medium

A. Circumference should not use Math.PI

B. Radius property is missing get accessor

C. Computed property Diameter cannot be assigned in set accessor

D. No error, code is correct

Solution

1. Step 1: Check computed property Diameter

   Diameter is read-only computed property with only get accessor (=>). It cannot be assigned a value.

2. Step 2: Analyze Circumference set accessor

   Circumference tries to set Diameter, which is not allowed because Diameter has no set accessor.

3. Final Answer:

   Computed property Diameter cannot be assigned in set accessor -> Option C

4. Quick Check:

   Read-only property cannot be set [OK]

Hint: Computed properties with => are read-only [OK]

Common Mistakes:

• Trying to set read-only computed properties
• Ignoring property accessors
• Confusing methods with properties

5. You want to create a computed property IsAdult in a Person class that returns true if Age is 18 or more, otherwise false. Which code correctly implements this?

hard

A. public bool IsAdult() { return Age >= 18; }

B. public bool IsAdult { get { return Age > 18; } }

C. public bool IsAdult { get; set; } = Age >= 18;

D. public bool IsAdult => Age >= 18;

Solution

1. Step 1: Understand requirement for computed property

   IsAdult should return true if Age is 18 or more, false otherwise, without storing a value.

2. Step 2: Check each option

   public bool IsAdult => Age >= 18; uses expression-bodied property correctly with >= 18. public bool IsAdult { get { return Age > 18; } } uses > 18 (wrong condition). public bool IsAdult { get; set; } = Age >= 18; tries to set property with Age comparison, which is invalid. public bool IsAdult() { return Age >= 18; } is a method, not a property.

3. Final Answer:

   public bool IsAdult => Age >= 18; -> Option D

4. Quick Check:

   Age >= 18 for IsAdult [OK]

Hint: Use => with condition for simple computed properties [OK]

Common Mistakes:

• Using > instead of >= for age check
• Trying to set computed property value
• Confusing methods with properties