Lesson 9: C# setup and .NET foundations: Architecture checkpoint

Concept Explanation

This lesson is a checkpoint on structure rather than syntax. By this point, you should start separating responsibilities instead of placing all logic in one file or one long method. A simple C# program becomes easier to test when input handling, core logic, and output are clearly divided. Here you will sketch a small console-style architecture, connect the pieces, and review why the layout matters. The main goal is to recognize when a program is still small enough to understand, but already large enough to benefit from better organization.

Where to Put the Code

1. Define color and position variables at the top.
2. Create shape drawing or placement logic in the middle.
3. Render output (print, canvas, SVG, or styled block) at the end.

Command Reference

• Identify which part of the example owns the business rule and which part only handles output.
• Move one responsibility into a separate method or class and check whether the flow is clearer.
• Change the rule inside the service without rewriting the program entry point.
• Describe why this structure is easier to test than putting everything directly in Main.

Step-by-step Guide

1. Read the sample once and label the role of each class or method.
2. Run the code and confirm that the service produces the final message.
3. Change one rule inside the service, such as formatting or trimming, and rerun the example.
4. Compare this layout with a version where all code lives in Main.
5. Finish by deciding whether the current structure is simple, clear, and easy to extend.

Practice Exercises

• Create a small service that formats order totals or user names instead of greetings.
• Add a second method to the service and decide whether it still belongs in the same class.
• Rewrite the sample with a helper method first, then compare it with the class-based version.

Coding Challenges

• Design a tiny console app with separate parts for reading input, applying logic, and printing output.
• Compare two structures for the same task and explain which one would be easier to grow later.

Mini Practice Tasks

• Rename one class or method to make its responsibility clearer.
• Add one small improvement without changing the overall structure.
• Write a one-line note explaining what this architecture is protecting you from.