13. C# (Project A : The Method Calculator)

A Small Project to Force Real Method Design

This project is intentionally simple.

But it has one strict rule:

You are not allowed to write everything inside Main.
You must separate logic into methods.

The goal is not math.

The goal is structure.

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Why This Project Matters

Many beginners write programs like this:

• All input
• All logic
• All printing

… inside Main.

It works.

But it builds a terrible habit.

This project forces you to:

• Think in terms of responsibilities
• Separate input from processing
• Separate processing from output
• Use parameters and return values correctly

If you cannot structure this small calculator properly,
you cannot structure larger systems later.

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System Flow

Your program must follow this exact flow.

1. Input

Ask the user for:

• Number 1
• Number 2

Use:

• Console.ReadLine()
• int.Parse()

You are responsible for converting the string input into integers.

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2. Select

Ask the user which operation they want to perform.

For example:

1. Add
2. Subtract
3. Get Remainder

This selection must influence which method is called.

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3. Process (This Is the Core)

Use an if statement to decide which method to call.

• If the user selects 1 → call Add(num1, num2)
• If the user selects 2 → call Subtract(num1, num2)
• If the user selects 3 → call GetRemainder(num1, num2)

Each method must:

• Receive two integers as parameters
• Return an integer result

No printing inside the calculation methods.

They must return, not print.

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4. Output

Take the value returned by the method
and print it in Main.

Processing and output must remain separate.

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Required Concepts

You must use:

• int.Parse
• Methods with parameters
• Methods with return values
• % (modulo operator for remainder)

If you skip any of these, you are skipping the point of the exercise.

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Design Constraints

To make this meaningful:

1. Do not duplicate calculation logic inside Main.
2. Do not print inside your math methods.
3. Do not hard-code numbers.
4. Do not collapse everything into one method.

If it feels slightly uncomfortable, you are probably doing it right.

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Why I Am Not Posting the Solution

Because the solution is not the goal.

The goal is:

• Thinking through structure
• Making mistakes
• Refactoring
• Understanding why separation matters

If you can build this cleanly,
you understand:

• Method design
• Return values
• Responsibility separation
• Basic program architecture

If you struggle, that is even better.

That struggle is the real exercise.