Property validation logic in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this property validation code?

Consider the following C# class with a property that validates input. What will be printed when the Main method runs?

C Sharp (C#)

using System;

class Person
{
    private int age;
    public int Age
    {
        get => age;
        set
        {
            if (value < 0 || value > 120)
                Console.WriteLine("Invalid age");
            else
                age = value;
        }
    }
}

class Program
{
    static void Main()
    {
        Person p = new Person();
        p.Age = 25;
        Console.WriteLine(p.Age);
        p.Age = -5;
        Console.WriteLine(p.Age);
    }
}

A 25\nInvalid age

B Invalid age\n0

C Invalid age\n25

D 25\nInvalid age\n25

💡 Hint

Think about when the age field is updated and when the message is printed.

The setter only updates the private field age if the value is valid. When setting -5, it prints "Invalid age" but does not change age. So the last printed age remains 25.

❓ Predict Output

intermediate

What error does this property validation code produce?

Examine this C# class with a property setter. What error will occur when compiling or running this code?

C Sharp (C#)

using System;

class Product
{
    private decimal price;
    public decimal Price
    {
        get { return price; }
        set
        {
            if (value < 0)
                throw new ArgumentException("Price cannot be negative");
            else
                Price = value;
        }
    }
}

A NullReferenceException at runtime

B StackOverflowException at runtime

C No error, runs fine

D Compile-time error: missing semicolon

💡 Hint

Look at how the setter assigns the value inside itself.

The setter calls Price = value; which calls the setter again, causing infinite recursion and a StackOverflowException at runtime.

🧠 Conceptual

advanced

Which property validation approach ensures thread safety?

You want to validate a property value and ensure that multiple threads can safely set and get it without causing inconsistent state. Which approach below best achieves this?

A Use a private field with lock statements in both getter and setter

B Use only a public auto-property with no validation

C Validate only in the constructor and make property read-only

D Use a static property with validation logic

💡 Hint

Think about how to prevent race conditions when multiple threads access the property.

Using a private field with lock in getter and setter ensures that only one thread accesses the field at a time, preventing inconsistent state.

🔧 Debug

advanced

Why does this property validation code fail to reject invalid input?

This C# class tries to reject negative values for the Score property, but it still allows negative values. Why?

C Sharp (C#)

using System;

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

A The private field is not initialized

B The setter is missing a return statement

C The if condition checks the old value instead of the new value

D The property should be static

💡 Hint

Check what variable the if condition is testing.

The condition if (score < 0) checks the current field value, not the new value value. So negative inputs are not caught.

🚀 Application

expert

How many items are in the dictionary after this property validation code runs?

This C# class uses a property with validation to add entries to a dictionary. After running the Main method, how many items are in the dictionary?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Registry
{
    private Dictionary<string, int> data = new();
    private int value;
    public int Value
    {
        get => value;
        set
        {
            if (value >= 0)
            {
                this.value = value;
                data[$"key{value}"] = value;
            }
        }
    }

    public int Count => data.Count;
}

class Program
{
    static void Main()
    {
        Registry r = new Registry();
        r.Value = 1;
        r.Value = 2;
        r.Value = -1;
        r.Value = 2;
        Console.WriteLine(r.Count);
    }
}

A 2

B 3

C 4

D 1

💡 Hint

Consider how dictionary keys behave when assigned multiple times.

The dictionary keys are "key1" and "key2" after valid assignments. The negative value is ignored. Assigning "key2" twice overwrites the same entry, so total count is 2.