Property validation logic in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a property with a private setter.

C Sharp (C#)

public class Person {
    public string Name { get; [1] }
}

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

Aprivate set

Bset

Cget set

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 'set' makes the setter public.

Using 'get set' allows public setting.

Using 'init' allows setting only during object initialization.

The property setter is made private by using private set, so it can only be set inside the class.

2fill in blank

medium

Complete the code to validate the Age property so it cannot be set below 0.

C Sharp (C#)

private int age;
public int Age {
    get { return age; }
    set {
        if ([1] < 0) throw new ArgumentException("Age cannot be negative");
        age = value;
    }
}

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

Athis.age

Bage

Cvalue

DAge

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name instead of 'value' in the condition.

Using the property name inside its own setter causes recursion.

The value keyword represents the value being assigned to the property. We check if it is less than 0.

3fill in blank

hard

Fix the error in the property setter to correctly validate and assign the value.

C Sharp (C#)

private string email;
public string Email {
    get { return email; }
    set {
        if (!value.Contains("@"))
            throw new ArgumentException("Invalid email");
        [1] = value;
    }
}

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

AEmail

Bemail

Cvalue

Dthis.Email

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning to the property inside its own setter causes infinite recursion.

Assigning to 'value' is invalid.

The private field email should be assigned the new value, not the property itself, to avoid infinite recursion.

4fill in blank

hard

Fill both blanks to create a property that validates the Score is between 0 and 100.

C Sharp (C#)

private int score;
public int Score {
    get { return score; }
    set {
        if ([1] < 0 || [2] > 100)
            throw new ArgumentOutOfRangeException("Score must be 0-100");
        score = value;
    }
}

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

Avalue

Bscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name instead of 'value' in the condition.

Checking the wrong variable for the range.

We check the new value being assigned (value) to ensure it is within the valid range.

5fill in blank

hard

Fill all three blanks to create a property with a backing field that validates non-empty strings and trims whitespace.

C Sharp (C#)

private string name;
public string Name {
    get { return name; }
    set {
        if (string.IsNullOrWhiteSpace([1]))
            throw new ArgumentException("Name cannot be empty");
        name = [2].Trim();
        Console.WriteLine($"Name set to: [3]", name);
    }
}

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

Avalue

Cname

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name inside its own setter causing recursion.

Using the wrong variable in the Console.WriteLine.

The setter uses value to check and trim the input. The name field is used in the console output.

Practice

1. What is the main purpose of adding validation logic inside a property setter in C#?

easy

A. To check and control the value before saving it to the field

B. To make the property read-only

C. To speed up the program execution

D. To automatically generate a default value

Solution

1. Step 1: Understand property setters

   Property setters allow you to assign values to private fields through a controlled interface.

2. Step 2: Role of validation logic

   Validation logic inside the setter checks if the value is valid before saving it, preventing invalid data.

3. Final Answer:

   To check and control the value before saving it to the field -> Option A

4. Quick Check:

   Validation in setter = control value before save [OK]

Hint: Validation logic in setter controls data before saving [OK]

Common Mistakes:

• Thinking validation makes property read-only
• Assuming validation speeds up code
• Confusing validation with default value assignment

2. Which of the following is the correct syntax to throw an exception inside a property setter when the value is invalid?

easy

A. set { if (value < 0) throw new Exception("Invalid value"); field = value; }

B. set { if (value < 0) return; field = value; }

C. set { if (value < 0) Console.WriteLine("Invalid"); field = value; }

D. set { if (value < 0) break; field = value; }

Solution

1. Step 1: Identify correct exception throwing syntax

   Throwing an exception uses the keyword 'throw' followed by 'new Exception(message)'.

2. Step 2: Check each option

   set { if (value < 0) throw new Exception("Invalid value"); field = value; } correctly throws an exception if value is less than zero. Others use invalid statements like return, Console.WriteLine, or break inside setter.

3. Final Answer:

   set { if (value < 0) throw new Exception("Invalid value"); field = value; } -> Option A

4. Quick Check:

   Throw exception = throw new Exception(...) [OK]

Hint: Use 'throw new Exception' to stop invalid values [OK]

Common Mistakes:

• Using 'return' instead of 'throw' in setter
• Trying to use 'break' inside setter
• Only printing error without stopping assignment

3. Consider this C# class snippet:

class Person {
  private int age;
  public int Age {
    get => age;
    set {
      if (value < 0) throw new ArgumentException("Age cannot be negative");
      age = value;
    }
  }
}

What happens if you run this code?
var p = new Person();
p.Age = -5;

medium

A. The age is set to -5 without error

B. An ArgumentException is thrown with message 'Age cannot be negative'

C. The program crashes with a NullReferenceException

D. The setter ignores the negative value and leaves age unchanged

Solution

1. Step 1: Analyze setter validation

   The setter checks if value is less than 0 and throws ArgumentException if true.

2. Step 2: Apply to given code

   Setting Age to -5 triggers the exception because -5 < 0.

3. Final Answer:

   An ArgumentException is thrown with message 'Age cannot be negative' -> Option B

4. Quick Check:

   Negative age triggers ArgumentException [OK]

Hint: Setter throws exception on invalid input [OK]

Common Mistakes:

• Assuming negative value is accepted
• Confusing exception type thrown
• Thinking setter silently ignores invalid values

4. Identify the error in this property setter code:

private string name;
public string Name {
  get { return name; }
  set {
    if (value == null || value == "")
      throw new ArgumentException("Name cannot be empty");
    name = value;
  }
}

medium

A. The setter does not assign the value to the field

B. The setter should use 'value.Equals("")' instead of 'value == ""'

C. The setter does not check for whitespace-only strings

D. The setter should not throw exceptions in property setters

Solution

1. Step 1: Review validation logic

   The setter checks if value is null or empty string but does not check if value is whitespace only.

2. Step 2: Understand missing validation

   Strings like " " (spaces) pass the check but are usually invalid for a name.

3. Final Answer:

   The setter does not check for whitespace-only strings -> Option C

4. Quick Check:

   Missing whitespace check in setter validation [OK]

Hint: Check for whitespace with string.IsNullOrWhiteSpace [OK]

Common Mistakes:

• Thinking '==' is wrong for string comparison here
• Believing exceptions should never be thrown in setters
• Forgetting to assign value to field

5. You want to create a property Score that only accepts values between 0 and 100 inclusive. If the value is outside this range, it should throw an ArgumentOutOfRangeException. Which of these implementations correctly applies this validation?

hard

A. private int score; public int Score { get => score; set { if (value < 0 && value > 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } }

B. private int score; public int Score { get => score; set { if (value <= 0 && value >= 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } }

C. private int score; public int Score { get => score; set { if (value > 0 || value < 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } }

D. private int score; public int Score { get => score; set { if (value < 0 || value > 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } }

Solution

1. Step 1: Understand the range condition

   The value must be between 0 and 100 inclusive, so invalid values are less than 0 or greater than 100.

2. Step 2: Analyze each condition

   private int score; public int Score { get => score; set { if (value < 0 || value > 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } } uses 'value < 0 || value > 100' which correctly checks invalid values. Options A, B, and D use incorrect logical operators or conditions.

3. Final Answer:

   private int score; public int Score { get => score; set { if (value < 0 || value > 100) throw new ArgumentOutOfRangeException("Score must be 0-100"); score = value; } } -> Option D

4. Quick Check:

   Use '||' for out-of-range checks [OK]

Hint: Use 'if (value < min || value > max)' for range validation [OK]

Common Mistakes:

• Using '&&' instead of '||' in range checks
• Reversing comparison operators
• Throwing wrong exception type