1. Computer Programming TCP1224 Chapter 2 Beginning the Problem-Solving Process

2. Week 1 Summary Programs: step-by-step instructions that tell a computer how to perform a task Programmers use programming languages to communicate with the computer ▫First programming languages were machine languages ▫High-level languages can be used to create procedure-oriented programs or object-oriented programs Algorithm: step-by-step instructions that accomplish a task (not written in a programming language) ▫Algorithms contain one or more of the following control structures: sequence, selection, and repetition 2

3. Week 1 Summary 3 main elements of programming ▫Sequence structure: process the instructions, one after another, in the order listed ▫Repetition structure: repeat one or more instructions until some condition is met ▫Selection structure: directs the computer to make a decision, and then to select an appropriate action based on that decision 3

4. Week 2 Objectives Explain the problem-solving process used to create a computer program Analyze a problem Complete an Input-Process-Output (IPO) chart (not Initial Public Offering) Plan an algorithm using pseudocode and flowcharts Desk-check (pen and paper check) an algorithm 4

5. Concept Lesson Problem Solving ▫Solving Everyday Problems Creating Computer Solutions to Problems ▫Analyzing the Problem ▫Planning the Algorithm ▫Desk-Checking the Algorithm The Gas Mileage Problem Summary 5

6. Problem Solving In this lecture, we will: ▫Explore the thought process followed when solving problems. All of us have a different way of solving things, take for example a simple 8 x 9 problem.  Some of us will memorize it.  Some of use will solve it by 8 x 10  80 – 8  72  Some of use will do 8 x 5 + 8 x 4 (‘coz we can’t remember our multiplication tables).  Some of us will go through those “songs” for multiplication tables during our primary school days. 6

7. Problem Solving In this lecture, we will: ▫Learn how to use a similar process to create a computer solution to a problem  Called a computer program.  Each of us will have a different approach, so sometimes programming is called an Art as some believe it isn’t a science!  We start with analyzing the problem, finding a solution and then only creating the program. 7

8. Solving Everyday Problems First step in solving a problem: analyze it ▫E.g., problem of being hungry Next, you plan, review, implement, evaluate, and modify (if necessary) the solution ▫E.g., if you are still hungry 8

9. Solving Everyday Problems (1 st attempt) 9

10. Solving Everyday Problems (modification) 10

11. Creating Computer Solutions to Problems Analysis tools: IPO charts, pseudocode/algorithm, flowcharts To desk-check or hand-trace, use pencil, paper, and sample data to walk through algorithm A coded algorithm is called a program 11

12. Creating Computer Solutions to Problems (continued) 12

13. Analyzing the Problem Analyze a problem to: ▫Determine the goal of solving it  Output ▫Determine the items needed to achieve that goal  Input Always search first for the output ▫Meaning, what does the customer want, or what are the answers to your problem. That’s the most important part. 13

14. Analyzing the Problem Always search first for the output (continue) ▫From knowing what you want for the answer, you can then determine what are the questions you need to ask (input) ▫And how you are going to use (process) the input to obtain the output. 14

15. Analyzing the Problem (continued) Consider you have the following simple requirements about what Sarah Martin wants. 15

16. IPO Charts Use an IPO chart to organize and summarize the results of a problem analysis ▫IPO: Input, Processing, and Output 16

17. Analyzing the Problem (continued) Reduce the amount of information you need to consider in your analysis: 17

18. IPO Charts (continued) First, the output … 18

19. IPO Charts (continued) 19 Then the input …

20. IPO Charts  Problem Analyzing Then you work out the processing required. 20

21. Analyzing the Problem (continued) But as mentioned, most requirements are incomplete! Worse than having too much information is not having enough information to solve problem: 21

22. Analyzing the Problem (continued) Distinguish between information that is missing and information that is implied: 22

23. Planning the Algorithm Algorithm: set of instructions that will transform the problem’s input into its output ▫Record it in the Processing column of the IPO chart Processing item: intermediate value used by algorithm when processing input into output 23

24. Planning the Algorithm (Con’t) Pseudocode is a tool programmers use to help them plan an algorithm ▫Short English statements ▫Indentation is important (as mentioned last week). 24

25. Planning the Algorithm (continued) 25

26. Planning the Algorithm (continued) Flowcharts are also used to plan an algorithm ▫Use standardized symbols ▫Symbols connected with flowlines ▫Oval: start/stop symbol ▫Rectangle: process symbol  Represents tasks such as calculations ▫Parallelogram: input/output symbol  Represents I/O tasks ▫Diamond: selection symbol  Represents decision 26

27. Planning the Algorithm (continued) 27

28. Planning the Algorithm (continued) A problem can have more than one solution: 28

29. Hints for Writing Algorithms 29 This problem specification is almost identical to the one shown earlier in Figure 2-4

30. Hints for Writing Algorithms 30 You may use a portion of a previous solution to solve current problem

31. Desk-Checking the Algorithm 31

32. Desk-Checking the Algorithm (con’t) 32

33. Desk-Checking the Algorithm (con’t) Valid data is data that the programmer is expecting the user to enter Invalid data is data that he or she is not expecting the user to enter You should (in reality, you MUST) test an algorithm with invalid data ▫Users may make mistakes when entering data ▫A good programmer can foresee what type of mistakes users make. 33

34. Summary Problem-solving typically involves analyzing the problem, and then planning, reviewing, implementing, evaluating, and modifying (if necessary) the solution Programmers use tools (IPO charts, pseudocode, flowcharts) to help them analyze problems and develop algorithms ▫During analysis, you determine the output and input ▫During planning, you write the steps that will transform the input into the output 34

35. Summary (continued) After the analysis and planning, you desk-check the algorithm ▫Follow each of the steps in algorithm by hand Coding refers to translating the algorithm into a language that the computer can understand Before writing an algorithm, consider whether you have already solved a similar problem 35

36. Homework Pass up the following as homework by next Tuesday's lab session. ▫California and Vermont are just names of places. ▫Gallons is about <4 litres (about 3.785 litres). ▫Gas is petrol (in US slang). Having the book may help here. You just need to do the flowchart for the algorithm section, that’s all … 36

37. The Gas Mileage Problem 37

38. The Gas Mileage Problem (continued) After planning the algorithm, you desk-check it: 38

39. Reading Chapter 3– Completing the Problem-Solving Process and Getting Started with C++ 39