1. Designing Programs

2. Approach Until Now Pick smallest meaningful step you can do Goto 1
Do it
Test it
Goto 1

3. New Approach Can I do it in ~10 lines? Yes: Do it No:
Break the problem down into smaller tasks
Define each in terms of input and output
With each task, go to 1

4. Reasons For Functions
Reuse code:

5. Reasons For Functions
Create abstractions:
Detailed Abstracted

6. When To Function Reusing same code in multiple locations
Want to provide abstraction
Existing code is too complex

7. How To Function
A good function
Does exactly one job

8. How To Function A good function Does exactly one job
Has clear inputs/outputs

9. How To Function A good function Does exactly one job
Has clear inputs/outputs
Is the right length
Probably Not
Maybe
Sure

10. Comparison
Monolithic vs Modular…

11. Stepwise Refinement Take problem Break into subproblems
With each subproblem: Can you implement it easily?
Yes : Done
No : Goto 1 with this problem

12. Building a Program
Goal: Display month calendar given year, month

13. Break Down

14. Break Down

15. Break Down

16. Break Down

17. Break Down

18. Break Down

19. Break Down

20. Bottom Up
Implement low level functions, test individually

21. Top Down
Implement top level functions using stubs for lower level ones

22. Real World Development is cyclical Make plan Code to plan Learn stuff
Goto 1