Access modifiers (public, private, internal) in C Sharp (C#) - Time & Space Complexity

Time Complexity: Access modifiers (public, private, internal)

O(1)

Understanding Time Complexity

When we use access modifiers like public, private, and internal, we control who can use parts of our code.

We want to understand how these choices affect the time it takes for the program to run.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Sample {
    private int secretNumber = 42;
    public int GetNumber() {
        return secretNumber;
    }
    internal void PrintNumber() {
        System.Console.WriteLine(secretNumber);
    }
}
    

This code defines a class with different access levels for its members.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: There are no loops or repeated operations here.
• How many times: Each method runs once when called.

How Execution Grows With Input

Since there are no loops or repeated steps, the time to run these methods stays the same no matter the input size.

Input Size (n)	Approx. Operations
10	Constant steps
100	Constant steps
1000	Constant steps

Pattern observation: The time does not grow with input size; it stays steady.

Final Time Complexity

Time Complexity: O(1)

This means the time to run these methods stays the same no matter how big the input is.

Common Mistake

[X] Wrong: "Making something private or internal makes the code slower because it adds checks."

[OK] Correct: Access modifiers only control who can use the code; they do not add extra steps that slow down the program.

Interview Connect

Understanding that access modifiers do not affect how fast code runs helps you focus on what really matters when writing efficient programs.

Self-Check

"What if the methods contained loops that depended on input size? How would the time complexity change?"

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