Lesson 9: C++ toolchain and basics: Architecture checkpoint

Concept Explanation

This lesson is about structure. Instead of placing every detail in one file, you will look at a tiny split between declaration and implementation and think about why that matters as a program grows. The goal is not to memorize build-system rules, but to understand responsibilities: where interfaces belong, where behavior belongs, and how that separation helps you test, reuse, and change code with less confusion. By the end, you should be able to describe a simple C++ layout where each file has a clear job and the whole example remains easy to navigate.

Where to Put the Code

1. Start with variables and inputs. Keep includes, main function, and data types explicit.
2. Add processing logic in the middle section.
3. Finish with output and quick validation.

Command Reference

• Describe the purpose of the header file in one sentence before you change any code.
• Modify the function name or behavior once, then update both declaration and definition consistently.
• Create a tiny main file mentally or on paper that would call add(2, 3).
• Record one reason separating interface from implementation becomes useful in larger projects.

Step-by-step Guide

1. Read both parts of the example and identify which file exposes the interface.
2. Explain what would break if the declaration and definition no longer matched.
3. Make one small change, such as renaming the function or adjusting the return expression, and keep the files in sync.
4. Check the layout again and confirm that each file still has one clear responsibility.
5. End with a short checklist covering naming, consistency, and ease of reuse.

Practice Exercises

• Add a second function declaration and definition for subtract while keeping the same file structure.
• Write a simple main.cpp example that includes the header and prints the result of one function call.
• Refactor the naming so the utility file sounds more specific to its purpose.

Coding Challenges

• Compare this split-file approach with a single-file version and explain which is easier to maintain as features grow.
• Design a tiny utility module with two related functions and keep the interface clean and minimal.

Mini Practice Tasks

• Add one extra function prototype to the header.
• Write a one-line summary of what this code organization achieves.
• Check that the declaration and definition use the same name and parameter order.