Complete missing implementations in challenge exercise files

[Copilot]

This PR completes all the missing implementations in the challenge exercise files throughout the C++ Programming Foundations course repository. Several challenge files contained stub implementations with "Write your code here" comments that needed to be completed for students to have working examples.

Changes Made

Completed 8 challenge exercise files:

• src/Ch02/02_13/CodeDemo.cpp - Data types challenge: Implemented add_int() function that casts floating-point parameters to integers and returns their sum
• src/Ch03/03_08/CodeDemo.cpp - Calculate average challenge: Implemented my_average() function that computes the average of three different integer types
• src/Ch04/04_11/CodeDemo.cpp - Vector manipulation challenge: Implemented SelectKeyPoints() function that extracts first, indexed, and last elements from a vector
• src/Ch05/05_09/CodeDemo.cpp - Resource cost calculation challenge: Implemented CalculateTotalCost() function with tax calculation logic for different resource types (Basic: 5%, Luxury: 15%, Essential: 0%)
• src/Ch06/06_07/CodeDemo.cpp - Rhythm game scores challenge: Implemented overloaded CalculateScore() functions with default parameters for millisecond and second-based scoring
• src/Ch07/07_05b/CodeDemo.cpp - Inventory class usage: Completed main function with proper inventory operations (add items, display, remove, check count, access by index)
• src/Ch07/07_10/CodeDemo.cpp - Person class design challenge: Implemented complete Person class with private members (name, energy, happiness, health) and public methods (Eat(), Play(), Sleep(), getters)
• src/Ch08/08_10/CodeDemo.cpp - Virtual pet schedule challenge: Implemented ManagePetSchedule() function using deque operations for pet activity management

Technical Details

All implementations follow the existing code style and patterns in the repository:

• Use C++17 standard features appropriately
• Include proper error handling and boundary checks
• Match the expected behavior from corresponding solution files
• Maintain consistent naming conventions and formatting

Testing

Each implementation has been thoroughly tested:

• All files compile successfully with g++ -std=c++17
• Each program produces the expected output when run
• Implementations match the logic and results from corresponding solution files

This ensures students have complete, working examples for all challenge exercises in the course.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.