Common bugs from reference sharing in C Sharp (C#) - Mini Project: Build & Apply

Common Bugs from Reference Sharing in C#

📖 Scenario: Imagine you are working on a simple inventory system for a small store. You have a list of products, and you want to create a copy of this list to apply discounts without changing the original list.This project will help you understand how sharing references between objects can cause unexpected bugs.

🎯 Goal: You will create a list of products, then create a copy of this list. You will apply a discount to the copied list and observe how changes affect the original list due to reference sharing.

📋 What You'll Learn

Create a list of products with exact names and prices

Create a copy of the product list by assigning it to a new variable

Apply a discount to the copied list by changing product prices

Print both original and copied lists to observe the effect of reference sharing

💡 Why This Matters

🌍 Real World

Understanding reference sharing helps prevent bugs in programs that manage collections of objects, like inventory systems, user lists, or game entities.

💼 Career

Many programming jobs require managing data structures carefully to avoid unintended side effects from shared references, especially in object-oriented languages like C#.

1

Create the original product list

Create a list called products containing three Product objects with these exact values: ("Apple", 100), ("Banana", 50), and ("Cherry", 75). Use the provided Product class.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Product
{
    public string Name;
    public int Price;

    public Product(string name, int price)
    {
        Name = name;
        Price = price;
    }
}

class Program
{
    static void Main()
    {
        // Create the products list with three Product objects
        // Your code here
    }
}

Hint

Use new List<Product> { ... } and add three new Product(name, price) objects inside the braces.

2

Create a copy of the product list by reference

Create a new variable called discountedProducts and assign it the value of products (this copies the reference, not the objects).

C Sharp (C#)

using System;
using System.Collections.Generic;

class Product
{
    public string Name;
    public int Price;

    public Product(string name, int price)
    {
        Name = name;
        Price = price;
    }
}

class Program
{
    static void Main()
    {
        List products = new List
        {
            new Product("Apple", 100),
            new Product("Banana", 50),
            new Product("Cherry", 75)
        };
        
        // Create discountedProducts by assigning products
        // Your code here
    }
}

Hint

Just assign discountedProducts = products; to copy the reference.

3

Apply a discount to the copied list

Use a for loop with variable i to go through discountedProducts and reduce each product's Price by 10%. Use integer division for simplicity.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Product
{
    public string Name;
    public int Price;

    public Product(string name, int price)
    {
        Name = name;
        Price = price;
    }
}

class Program
{
    static void Main()
    {
        List products = new List
        {
            new Product("Apple", 100),
            new Product("Banana", 50),
            new Product("Cherry", 75)
        };
        
        List discountedProducts = products;
        
        // Apply 10% discount to each product in discountedProducts
        // Your code here
    }
}

Hint

Use a for loop from 0 to discountedProducts.Count and update the Price by multiplying by 90 and dividing by 100.

4

Print both lists to observe the effect

Use two foreach loops to print the Name and Price of each product in products and discountedProducts. Print "Original products:" before the first list and "Discounted products:" before the second list.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Product
{
    public string Name;
    public int Price;

    public Product(string name, int price)
    {
        Name = name;
        Price = price;
    }
}

class Program
{
    static void Main()
    {
        List products = new List
        {
            new Product("Apple", 100),
            new Product("Banana", 50),
            new Product("Cherry", 75)
        };
        
        List discountedProducts = products;
        
        for (int i = 0; i < discountedProducts.Count; i++)
        {
            discountedProducts[i].Price = discountedProducts[i].Price * 90 / 100;
        }
        
        // Print original and discounted products
        // Your code here
    }
}

Hint

Use Console.WriteLine to print the headers and product details. Notice that both lists show the discounted prices because they share the same references.

Practice

1. What happens when you assign one object variable to another in C#?

easy

A. Both variables refer to the same object in memory.

B. A new independent copy of the object is created automatically.

C. The original object is deleted and replaced by the new variable.

D. The variables become unrelated and hold different objects.

Solution

1. Step 1: Understand object assignment in C#

   Assigning one object variable to another copies the reference, not the object itself.

2. Step 2: Effect of reference copying

   Both variables point to the same object in memory, so changes via one affect the other.

3. Final Answer:

   Both variables refer to the same object in memory. -> Option A

4. Quick Check:

   Reference copy = same object [OK]

Hint: Assigning objects copies references, not objects [OK]

Common Mistakes:

• Thinking a new object is created automatically
• Assuming variables hold independent objects
• Confusing value types with reference types

2. Which of the following is the correct way to create a copy of an object to avoid reference sharing in C#?

easy

A. Use a method like MemberwiseClone() or implement ICloneable.

B. Use the assignment operator (=) between two object variables.

C. Declare the object variable as readonly.

D. Use the 'new' keyword without copying fields.

Solution

1. Step 1: Identify how to copy objects in C#

   Assignment copies references, so to create a copy, you need cloning methods like MemberwiseClone() or ICloneable.

2. Step 2: Why other options are incorrect

   Assignment operator copies reference; readonly only prevents reassignment; 'new' without copying fields creates a new empty object.

3. Final Answer:

   Use a method like MemberwiseClone() or implement ICloneable. -> Option A

4. Quick Check:

   Clone method = copy object [OK]

Hint: Clone objects to avoid shared references [OK]

Common Mistakes:

• Using assignment operator expecting a copy
• Confusing readonly with copying
• Creating new object without copying data

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

class Box { public int Value; }
var box1 = new Box { Value = 5 };
var box2 = box1;
box2.Value = 10;
Console.WriteLine(box1.Value);

medium

A. 5

B. Compilation error

C. 0

D. 10

Solution

1. Step 1: Understand reference assignment in the code

   box2 is assigned box1, so both refer to the same Box object.

2. Step 2: Effect of changing box2.Value

   Changing box2.Value to 10 changes the single shared object, so box1.Value also becomes 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Shared reference means value changes reflect [OK]

Hint: Changing one reference changes all pointing to same object [OK]

Common Mistakes:

• Expecting box1.Value to remain 5
• Confusing value and reference types
• Assuming box2 is a separate object

4. Identify the bug in this C# code snippet related to reference sharing:

class Person { public string Name; }
var p1 = new Person { Name = "Alice" };
var p2 = p1;
p2.Name = "Bob";
Console.WriteLine(p1.Name);

medium

A. p1 and p2 refer to different objects, so no bug.

B. p2.Name change affects p1.Name because both reference the same object.

C. The code causes a null reference exception.

D. The assignment operator creates a deep copy automatically.

Solution

1. Step 1: Analyze object references in the code

   p2 is assigned p1, so both variables point to the same Person object.

2. Step 2: Effect of modifying p2.Name

   Changing p2.Name to "Bob" changes the shared object, so p1.Name also becomes "Bob".

3. Final Answer:

   p2.Name change affects p1.Name because both reference the same object. -> Option B

4. Quick Check:

   Shared reference causes shared changes [OK]

Hint: Check if variables share the same object reference [OK]

Common Mistakes:

• Assuming p1.Name remains "Alice"
• Expecting automatic deep copy on assignment
• Thinking null reference exception occurs

5. You want to create two independent lists of integers in C# so that modifying one list does not affect the other. Which code snippet correctly avoids reference sharing?

hard

A. var list1 = new List<int> {1, 2, 3}; var list2 = list1; list2.Add(4);

B. var list1 = new List<int> {1, 2, 3}; var list2 = list1; list1.Clear();

C. var list1 = new List<int> {1, 2, 3}; var list2 = new List<int>(list1); list2.Add(4);

D. var list1 = new List<int> {1, 2, 3}; var list2 = list1; list1 = new List<int>();

Solution

1. Step 1: Understand reference sharing with lists

   Assigning list2 = list1 copies the reference, so both variables point to the same list.

2. Step 2: Creating an independent copy

   Using new List<int>(list1) creates a new list copying elements, so list2 is independent.

3. Final Answer:

   var list2 = new List<int>(list1); list2.Add(4); -> Option C

4. Quick Check:

   New list constructor copies elements [OK]

Hint: Use new List<T>(existingList) to copy lists [OK]

Common Mistakes:

• Assigning list2 = list1 expecting copy
• Clearing list1 expecting list2 unaffected
• Reassigning list1 does not affect list2 reference