Access modifiers (public, private, internal) in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Access modifiers (public, private, internal)

Start

↓

Define class members

↓

Apply access modifiers

↓

public: accessible anywhere

↓

private: accessible only inside class

↓

internal: accessible inside same assembly

↓

Use members

↓

Access allowed?

Yes/No↓

End

This flow shows how class members are defined with access modifiers and how access is checked based on modifier rules.

Execution Sample

C Sharp (C#)

class MyClass {
  public int a = 1;
  private int b = 2;
  internal int c = 3;
}

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

Defines a class with public, private, and internal members and accesses the public member from outside.

Execution Table

Step	Action	Member Accessed	Access Modifier	Access Allowed	Output/Result
1	Create object obj	N/A	N/A	N/A	obj created
2	Access obj.a	a	public	Yes	Prints 1
3	Access obj.b	b	private	No	Compile error: 'b' is inaccessible
4	Access obj.c	c	internal	Yes if same assembly, else No	Prints 3 or error
5	End	N/A	N/A	N/A	Execution stops

💡 Execution stops after access attempts; private member access fails outside class.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
obj	null	MyClass instance	MyClass instance	MyClass instance	MyClass instance
obj.a	N/A	1	1	1	1
obj.b	N/A	2 (private)	2 (private)	2 (private)	2 (private)
obj.c	N/A	3 (internal)	3 (internal)	3 (internal)	3 (internal)

Key Moments - 3 Insights

Why can't we access the private member 'b' from outside the class?

Because 'b' is marked private, it is only accessible inside the class. The execution_table row 3 shows the compile error when trying to access it outside.

When can we access the internal member 'c'?

The internal member 'c' can be accessed anywhere inside the same assembly (project). If accessed from outside the assembly, access is denied as shown in execution_table row 4.

What does the public modifier allow?

Public members like 'a' can be accessed from anywhere, inside or outside the class and assembly, as shown in execution_table row 2.

Visual Quiz - 3 Questions

Look at the execution_table, what happens when we try to access obj.b?

A Compile error because 'b' is private

B Access is allowed and value 2 is printed

C Access is allowed only inside the same assembly

D Value 3 is printed

💡 Hint

Check execution_table row 3 where accessing obj.b causes a compile error.

At which step does the program print the value of the public member?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at execution_table row 2 where obj.a is accessed and prints 1.

If the internal member 'c' is accessed from a different assembly, what will happen?

A Access allowed and prints 3

B Compile error due to internal access restriction

C Compile error due to private access

D Access allowed only if public

💡 Hint

Refer to execution_table row 4 explaining internal access depends on assembly.

Concept Snapshot

Access modifiers control who can use class members:
- public: accessible anywhere
- private: accessible only inside the class
- internal: accessible inside the same assembly
Use modifiers to protect or expose data safely.

Full Transcript

This visual execution shows how access modifiers in C# control access to class members. Public members can be accessed anywhere, private members only inside the class, and internal members only inside the same assembly. The example creates an object and tries to access members with different modifiers. Access to private members from outside causes a compile error. Internal members are accessible only if accessed within the same assembly. This helps protect data and control visibility in programs.

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