Access modifiers (public, private, internal) in C Sharp (C#) - Mini Project: Build & Apply

Access Modifiers in C#

📖 Scenario: You are creating a simple class to represent a bank account. You want to control how the account's balance can be accessed and changed by using access modifiers.

🎯 Goal: Build a C# class BankAccount that uses public, private, and internal access modifiers to protect and expose data correctly.

📋 What You'll Learn

Create a class called BankAccount with a private field for balance

Add a public method to deposit money

Add an internal method to display the balance

Add a public method to withdraw money with balance check

💡 Why This Matters

🌍 Real World

Access modifiers help protect sensitive data and control how parts of a program interact, like keeping bank account balances safe.

💼 Career

Understanding access modifiers is essential for writing secure and maintainable code in professional software development.

1

Create the BankAccount class with a private balance field

Create a class called BankAccount with a private decimal field named balance initialized to 0.

C Sharp (C#)

class BankAccount
{
    // Your code here
}

Hint

Use private decimal balance = 0m; inside the class.

2

Add a public method to deposit money

Add a public method called Deposit that takes a decimal parameter amount and adds it to the private balance.

C Sharp (C#)

class BankAccount
{
    private decimal balance = 0m;

    // Your code here
}

Hint

Use public void Deposit(decimal amount) and add amount to balance.

3

Add an internal method to display the balance

Add an internal method called DisplayBalance that returns the current balance as a decimal.

C Sharp (C#)

class BankAccount
{
    private decimal balance = 0m;

    public void Deposit(decimal amount)
    {
        balance += amount;
    }

    // Your code here
}

Hint

Use internal decimal DisplayBalance() to return balance.

4

Add a public method to withdraw money with balance check and print the balance

Add a public method called Withdraw that takes a decimal amount. It should subtract amount from balance only if balance is enough. Then, create a BankAccount object, deposit 100, withdraw 30, and print the balance using DisplayBalance().

C Sharp (C#)

class BankAccount
{
    private decimal balance = 0m;

    public void Deposit(decimal amount)
    {
        balance += amount;
    }

    internal decimal DisplayBalance()
    {
        return balance;
    }

    // Your code here
}

// Your code here

Hint

Use public void Withdraw(decimal amount) with an if to check balance. Then create BankAccount object, deposit 100, withdraw 30, and print balance.

Practice

1.

Which access modifier allows a class member to be accessed from any other code in the same project or assembly?

easy

A. internal

B. private

C. public

D. protected

Solution

1. Step 1: Understand the meaning of internal

   The internal modifier allows access within the same assembly or project but not outside it.

2. Step 2: Compare with other modifiers

   private restricts access to the same class only, public allows access from anywhere, and protected allows access in derived classes.

3. Final Answer:

   internal -> Option A

4. Quick Check:

   Access inside project = internal [OK]

Hint: Internal means accessible only within the same project [OK]

Common Mistakes:

• Confusing internal with public
• Thinking private allows access outside class
• Mixing protected with internal

2.

Which of the following is the correct way to declare a private integer field named count in a class?

?

easy

A. internal count int;

B. int private count;

C. public int count;

D. private int count;

Solution

1. Step 1: Recall correct syntax for access modifiers

   The access modifier comes first, then the type, then the variable name.

2. Step 2: Check each option's order and keywords

   private int count; follows correct order: private int count;. Others have incorrect order or missing type.

3. Final Answer:

   private int count; -> Option D

4. Quick Check:

   Access modifier + type + name [OK]

Hint: Access modifier always comes before type in declaration [OK]

Common Mistakes:

• Placing access modifier after type
• Omitting the type
• Using invalid order of keywords

3.

Consider the following code snippet:

class MyClass {
    private int secret = 42;
    public int GetSecret() {
        return secret;
    }
}

MyClass obj = new MyClass();
Console.WriteLine(obj.secret);

What will happen when this code runs?

medium

A. Runtime error: NullReferenceException

B. It prints 42

C. Compilation error: 'secret' is inaccessible due to its protection level

D. It prints 0

Solution

1. Step 1: Identify access modifier of 'secret'

   The field secret is declared private, so it cannot be accessed outside MyClass.

2. Step 2: Check code accessing 'secret'

   The code tries to access obj.secret outside the class, which is not allowed and causes a compile-time error.

3. Final Answer:

   Compilation error: 'secret' is inaccessible due to its protection level -> Option C

4. Quick Check:

   Private fields cannot be accessed outside class [OK]

Hint: Private members cannot be accessed from outside their class [OK]

Common Mistakes:

• Assuming private fields are accessible outside class
• Confusing runtime errors with compile errors
• Thinking public methods expose private fields directly

4.

Given this code snippet, identify the error and fix it:

class Sample {
    internal int value;
}

class Test {
    void Show() {
        Sample s = new Sample();
        Console.WriteLine(s.value);
    }
}

Assuming these classes are in different projects, what is the problem?

medium

A. No error, code runs fine

B. Error: 'value' is inaccessible due to protection level; fix by changing 'internal' to 'public'

C. Error: 'value' must be private; fix by changing 'internal' to 'private'

D. Error: 'value' must be static; fix by adding 'static' keyword

Solution

1. Step 1: Understand 'internal' access modifier scope

   internal allows access only within the same project or assembly.

2. Step 2: Check class locations

   Since Sample and Test are in different projects, Test cannot access internal members of Sample.

3. Step 3: Fix the access level

   Changing value to public allows access from other projects.

4. Final Answer:

   Error: 'value' is inaccessible due to protection level; fix by changing 'internal' to 'public' -> Option B

5. Quick Check:

   Internal = same project only; public = accessible everywhere [OK]

Hint: Internal limits access to same project; use public for cross-project [OK]

Common Mistakes:

• Assuming internal allows cross-project access
• Changing internal to private incorrectly
• Confusing static with access modifiers

5.

You have a class library project with a class Helper that has a method Calculate() marked as internal. You want to allow another project in the same solution to use Calculate() without making it public. What is the best way to achieve this?

hard

A. Use the InternalsVisibleTo attribute to expose internal members to the other project

B. Change the method to public

C. Change the method to private and create a public wrapper

D. Move the method to the other project

Solution

1. Step 1: Understand internal and project boundaries

   internal restricts access to the same assembly, so other projects cannot access it by default.

2. Step 2: Use InternalsVisibleTo attribute

   This attribute allows you to specify friend assemblies that can access internal members without making them public.

3. Step 3: Evaluate other options

   Changing to public exposes to all, private hides too much, moving method is impractical.

4. Final Answer:

   Use the InternalsVisibleTo attribute to expose internal members to the other project -> Option A

5. Quick Check:

   InternalsVisibleTo grants internal access to specific projects [OK]

Hint: Use InternalsVisibleTo to share internal members across projects [OK]

Common Mistakes:

• Making method public unnecessarily
• Thinking private allows cross-project access
• Moving code instead of using attributes