Tutorial #7 Flowcharts (reprise)

1. Tutorial #7Flowcharts (reprise) Program Design

2. Introduction • We mentioned it already, that if we thing of an analyst as being analogous to an architect, and a developer as being analogous to a builder, then the most important thing we can do as analysts is to explain our designs to the developers in a simple and clear way. • How do architects do this?

4. Symbols

5. Symbols

6. Symbols Decision Terminal Input/Output Operation Connector Module Process

7. Flowcharts • So we start the program as: START

8. Flowcharts • Our program will finish with the following: END

9. SEQUENCE

10. Flowcharts • When we write programs, we assume that the computer executes the program starting at the beginning and working its way to the end. • This is a basic assumption of all algorithm design.

11. Flowcharts • When we write programs, we assume that the computer executes the program starting at the beginning and working its way to the end. • This is a basic assumption of all algorithm design. • We call this SEQUENCE.

12. START Statement1 Statement2 END

13. SELECTION

14. Flowcharts • What if we want to make a choice, for example, do we want to add sugar or not to the tea?

15. Flowcharts • What if we want to make a choice, for example, do we want to add sugar or not to the tea? • We call this SELECTION.

16. START Is Sugar required? Add Sugar Don’t Add Sugar No Yes END

17. ITERATION

18. Flowcharts • What if we need to tell the computer to keep doing something until some condition occurs?

19. Flowcharts • What if we need to tell the computer to keep doing something until some condition occurs? • Let’s say we wish to indicate that the you need to keep filling the kettle with water until it is full.

20. Flowcharts • What if we need to tell the computer to keep doing something until some condition occurs? • Let’s say we wish to indicate that the you need to keep filling the kettle with water until it is full. • We need a loop, or ITERATION.

21. START Keep Filling Kettle Kettle is not full? No Yes END

22. EXAMPLES

23. Flowcharts • So let’s say we want to express the following algorithm: • Read in a number and print it out.

24. START

25. START Read in A

26. START Read in A Print A

27. START Read in A Print A END

28. Flowcharts • So let’s say we want to express the following algorithm: • Read in a number and print it out double the number.

29. START

30. START Read in A

31. START Read in A Print A*2

32. START Read in A Print A*2 END

33. Or alternatively...

34. START

35. START Read in A

36. START Read in A B = A*2

37. START B = A * 2 can be read as “B gets the value of A multiplied by 2” Read in A B = A*2

38. START Read in A B = A*2 Print B

39. START Read in A B = A*2 Print B END

40. Flowcharts • So let’s say we want to express the following algorithm: • Read in a number, check if it is odd or even.

41. START

42. START Read in A

43. START Read in A Does A/2 give a remainder?

44. START Read in A Does A/2 give a remainder? Print “It’s Odd” Yes

45. START Read in A Does A/2 give a remainder? Print “It’s Odd” Print “It’s Even” No Yes

46. START Read in A Does A/2 give a remainder? Print “It’s Odd” Print “It’s Even” No Yes END

47. Flowcharts • So let’s say we want to express the following algorithm to print out the bigger of two numbers: • Read in two numbers, call them A and B. Is A is bigger than B, print out A, otherwise print out B.

48. START

49. START Read in A and B

50. START Read in A and B A>B?