หลักการโปรแกรม เพื่อแก้ปัญหาโดยใช้คอมพิวเตอร์

1. หลักการโปรแกรมเพื่อแก้ปัญหาโดยใช้คอมพิวเตอร์หลักการโปรแกรมเพื่อแก้ปัญหาโดยใช้คอมพิวเตอร์ อ.จรรยา สายนุ้ย CS.313 ภาควิชาวิทยาการคอมพิวเตอร์

2. Outline • Problem Solving • Definition • Problem • Problem Solving • Strategies • Techniques • Tools • Approach • Programming Principle • Programming Language • Programming Design • Programming Paradigms

3. Problem Solving Definition • Problem ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ • Problem Solving The process of transforming the description of a problem into the solution of that problem by using own knowledge of the problem domainand be relying on the ability to select and use appropriate problem solvingstrategies, techniques and tools

4. Problem Domain • sciences : mathematics , statistics , chemistry , physics, biology • business : inventory , accounting • education : registration , evaluation • banking : ATM , loaning , report • others : restaurant , transportation , hotel , department store

5. Problem Solving Strategies (Algorithm Design Techniques) • Divide and Conquer • Dynamic Programming • Greedy Algorithms • etc.

6. Problem Solving Techniques • Top-down Stepwise Refinement • Structured Programming • Modular Design • Bottom-up Approach • Recursion

7. Problem Solving Tools • Pseudo Code • Flowchart • Programming Languages • Editor • Debugger

8. Problem Solving Approach • Software Development Method or Software Life Cycle • Use computers in problem solving consists of 6 steps : • Requirement Specification • Analysis • Design • Implementation • Testing And Verification • Documentation

9. Software Life Cycle • Requirement Specification • what the problem is • what is needed to solve • what the solution should provide • any constraints and special conditions to concern • depend on familiarity with the problem domain

10. Software Life Cycle • Analysis • Input • Output • Constraints/Conditions • Formulas

11. Software Life Cycle 3.1 Algorithm design • definition • requirement • strategy • techniques 3.2 Data design • Input/Output • Process • Types • Representation • Structure • manipulation • Design

12. Software Life Cycle 3.1Algorithm design • Algorithm Definition Algorithm: a method of solution described as a sequence of steps to be performed in a specific logical order.

13. Software Life Cycle 3.1Algorithm design • Satisfied Requirements : • Unambiguousness • Generality • Correctness • Finiteness

14. Software Life Cycle 3.1Algorithm design • Representation Strategy • Pseudocoding • Flowcharting • HIPO Chart

15. Software Life Cycle 3.1Algorithm design • Techniques • Greedy Method • Divide and Conquer • Dynamic Programming • Backtracking Algorithms • etc.

16. Software Life Cycle 3.2 Data design • Input/Output • Process • Types : constant/variables ,global/local • Representation: number , text , etc. • Structure: array, file , queue , tree , etc. • Manipulation: operators , functions ................................................................................................................................................................ ................................................................................................................................................ ......................................................................................................................................................................... .....................................................................................................................................................

17. Software Life Cycle • Implementation or Coding • Programming Languages • writability • readability • modifiability • reusability

18. Software Life Cycle • Implementation or Coding • Important as designing skill • programming is the art of designing efficient algorithms to meet requirements • Programming errors • Debugging techniques • Strategies for defensive • Programming

19. Software Life Cycle • Implementation or Coding • Programming Errors • design errors • syntax/compilation errors • linker errors • run-time errors • warning diagnostic message

20. Software Life Cycle • Implementation or Coding • Debugging techniques • The ability to debug programs is another problem-solving skill that is as important as the ability to design programs • Debugging is the process of finding and correcting errors in computer programs

21. Software Life Cycle • Implementation or Coding • Debugging techniques • design errors • quite difficult to debug , no error message , incorrect output sometimes • incorrect formula , wrong program logic , inappropriate data type • careful review in analysis and design , use variety of testing data

22. Software Life Cycle • Implementation or Coding • Debugging techniques • syntax/compilation errors • Detect by compilers • Something missing / undeclared var. • Easy , just correct error sources • warning diagnostic message • Strange but can still proceed • Unreferenced var. • Get rid of causes or ignore

23. Software Life Cycle • Implementation or Coding • Debugging techniques • linker errors • Some errors prevent the linker to create the executable module • Function prototypes do not match their definitions • solution: correct prototypes

24. Software Life Cycle • Implementation or Coding • Debugging techniques • run-time/execution errors • while executing , difficult to debug, abnormal termination • divide by zero , type mismatch ,index is out of range, domain error • trace/step watch some variables’ value , error handling

25. Software Life Cycle • Implementation or Coding • Strategies for defensive • correction : errors debug • defence : to prevent abnormal termination /errors preparing to manage errors if (a < o) { … } using exception handler

26. Software Life Cycle • Testing And Verification • program verification • the process of ensuring that a program meets user requirements • one of the techniques that can be used for program verification is program testing

27. Software Life Cycle • Testing And Verification • program testing • the process of executing a program to demonstrate its correctness • testing methods • test data • testing modules : driver , stub • top-down testing • bottom-up testing • blackbox .vs. whitebox

28. Software Life Cycle: Example • Requirement Specification • เขียนโปรแกรมหาระยะทางระหว่างจุด 2 จุดคือ (x1 ,y1 ) และ (x2 ,y2 ) • สูตรคือ

29. Software Life Cycle : Example • Analysis • Input: integer x1 , y1 , x2 และ y2 • Output : float & positive value • Formulas :

30. Software Life Cycle: Example • Algorithm Design Pseudocode • Read x1 , y1 , x2 , y2 • dist = sqrt((x1 - x2)2 + (y1 - y2)2) • Write dist • end

31. Software Life Cycle: Example • Implementation or Coding #include <stdio.h> #include <math.h> void main() { int x1, x2, y1, y2; float dist; scanf(“%d %d %d %d”, &x1, &y1, &x2, &y2); dist = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); printf(“distance = %f\n”,dist); }

32. Software Life Cycle: Example • Testing And Verification • verifying: compile and debug • data test: 3 0 0 4 • output: 5.0

33. Software Life Cycle • Documentation • System documentation • Program documentation • User documentation

34. Software Life Cycle • Documentation • System documentation • Context Diagram • Dataflow Diagram • Database Design : E-R diagram , Relational model , Data dictionary • System modules/flowchart

35. Software Life Cycle • Documentation • Program documentation • Flowchart / Pseudocode • Program Listing • Sufficient in-program : comment , indentation

36. Software Life Cycle • Documentation • User documentation • Interfaces • Input Examples • Output Examples • Error messages : causes & effect

37. Programming Principles • Programming Languages • Program Design • Programming Paradigms

38. Programming Languages • Why programming languages ? • to enable the user to enlist the help of a computer in solving problems in the domain of interest • to enable the user to bridge the gap between problem and machine domain

39. Program Design • modular design • top-down approach • bottom-up approach • stepwise refinement • structured programming • etc.

40. Programming paradigms • imperative paradigm • functional paradigm • logic paradigm • object-oriented paradigm

41. Practice make perfect