Pseudocode Structure 5th October 2018

Transcription

1 Pseudocode Structure 5 th October 2018

2 Unit 1 Objective To apply language set of rules in writing Algorithm Learning outcome Students are expected to apply symbols to write algorithm in flowchart diagram

3 Section1: Pseudocode fundamentals? Section2: Type 2: Pseudocode Algorithm Structure

4 Pseudo means imitation or false and code refers to the instructions written in a programming language. Pseudocode is another programming analysis tool that is used for planning a program. Pseudocode is also called Program Design Language (PDL).

5 By Wikipedia definition: Pseudocode is a compact and informal highlevel (read to understand) description of a computer programming algorithm that uses the structural conventions of some programming language, but is intended for human reading rather than machine reading.

6 Pseudocode is made up of the following logic structures that have been proved to be sufficient for writing any computer program: Sequence Logic Selection Logic Iteration Logic

7 For looping and selection, The keywords that are to be used include Do While...EndDo; Do Until...Enddo; Case...EndCase; If...Endif; Call... with (parameters); Call; Return...; Return; When; Always use scope terminators for loops and iteration. As verbs, use the words Generate, Compute, Process, etc. Words such as set, reset, increment, compute, calculate, add, sum, multiply,... print, display, input, output, edit, test, etc. with careful indentation tend to foster desirable pseudocode.

8 In summary: Write only one statement per line. Capitalized initial keyword. Indent to show hierarchy. End multi-line structures. Keep statement language independent.

9 These are: Number each instruction. This is to enforce the notion, well-ordered collection of... operations. Each instruction should be unambiguous. It means the computing agent, in this case the reader, should be capable of carrying out the instructions. And also, each instruction should be effectively computable (do-able). Completeness. Nothing should be left out.

10 Following are some of the advantages of using pseudocode: Converting a pseudocode to a programming language is much more easier than converting a flowchart. As compared to flowchart, it is easier to modify a pseudocode of a program logic when program modifications are necessary.

11 It also suffers from some of the limitations. These limitations are as follows: In the cases of pseudocode, a graphic representation of program logic is not available. There are no standard rules to follow for using a pseudocode. Different programmers use their own style of writing pseudocode and hence, communication problem occurs due to lack of standardization.

12 To symbolize the arithmetic operators we use these symbols: Note: There is a precedence or hierarchy implied in this symbols.

13 When we have to make a choice between actions, we almost always base that choice on a test. There is a universally accepted set of symbols used to represent these phrases:

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16 Application of Set of Rules 1. Sequence (methodical/logical Flow step by step) 2. Selection (If statements) 3. Iteration/Loop/While statement

17 The first thing we do when designing a program is to decide on a name for the program.

18 The first thing we do when designing a program is to decide on a name for the program. Let s say we want to write a program to calculate interest, a good name for the program would be CalculateInterest.

19 The first thing we do when designing a program is to decide on a name for the program. Let s say we want to write a program to calculate interest, a good name for the program would be CalculateInterest. Note the use of CamelCase.

20 The first thing we do when designing a program is to decide on a name for the program. Let s say we want to write a program to calculate interest, a good name for the program would be CalculateInterest. Note the use of CamelCase.

21 So we start the program as: PROGRAM CalculateInterest:

22 So we start the program as: PROGRAM CalculateInterest: And in general it s: PROGRAM <ProgramName>:

23 Our program will finish with the following: END.

24 Our program will finish with the following: END. And in general it s the same: END.

25 So the general structure of all programs is: PROGRAM <ProgramName>: <Do stuff> END.

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27 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.

28 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.

29 In Pseudo code it looks like this: Statement1; Statement2; Statement3; Statement4; Statement5; Statement6; Statement7; Statement8;

30 Example: Preparation of a cup of tea: Write a Pseudocode for a developer to create a mobile app to simulate/show users how to prepare tea. General Logical Sequence Application: You do not jump from 1 to 6 before step 2 Organise everything together; Plug in kettle; Put teabag in cup; Put water into kettle; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk and/or sugar; Serve;

31 Or as a program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; Put water into kettle; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk and/or sugar; Serve; END.

32 Or as a program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; Put water into kettle; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk and/or sugar; Serve; END.

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34 What if we want to make a choice, for example, do we want to add sugar or not to the tea?

35 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.

36 So, we could state this as: IF (sugar is required) THEN add sugar; ELSE don t add sugar; ENDIF;

37 Or, in general: IF (<CONDITION>) THEN <Statements>; ELSE <Statements>; ENDIF;

38 Or to check which number is biggest: IF (A > B) THEN Print A + is bigger ; ELSE Print B + is bigger ; ENDIF;

39 Adding a selection statement in the program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; Put water into kettle; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk; IF (sugar is required) THEN add sugar; ELSE do nothing; ENDIF; Serve; END.

40 Adding a selection statement in the program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; Put water into kettle; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk; IF (sugar is required) THEN add sugar; ELSE do nothing; ENDIF; Serve; END.

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42 What if we need to tell the computer to keep doing something until some condition occurs?

43 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.

44 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.

45 So, we could state this as: WHILE (Kettle is not full) DO keep filling kettle; ENDWHILE;

46 Or, in general: WHILE (<CONDITION>) DO <Statements>; ENDWHILE;

47 Or to print out the numbers 1 to 5: A = 1; WHILE(A < 5) DO Print A; A = A + 1; ENDWHILE;

48 What is the benefit of using a loop?

49 Consider the problem of searching for an entry in a phone book with only condition:

50 Consider the problem of searching for an entry in a phone book with only condition: Get first entry If this is the required entry Then write down phone number Else get next entry If this is the correct entry then write done entry else get next entry if this is the correct entry.

51 This could take forever to specify.

52 This could take forever to specify. There must be a better way to do it.

53 We may rewrite this as follows: Get first entry; Call this entry N; WHILE N is NOT the required entry DO Get next entry; Call this entry N; ENDWHILE;

54 We may rewrite this as follows: Get first entry; Call this entry N; WHILE N is NOT the required entry DO Get next entry; Call this entry N; ENDWHILE; This makes loops essential!

55 Or as a program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; WHILE (Kettle is not full) DO keep filling kettle; ENDWHILE; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk; IF (sugar is required) THEN add sugar; ELSE do nothing; ENDIF; Serve; END.

56 Or as a program: PROGRAM MakeACupOfTea: Organise everything together; Plug in kettle; Put teabag in cup; WHILE (Kettle is not full) DO keep filling kettle; ENDWHILE; Wait for kettle to boil; Add water to cup; Remove teabag with spoon/fork; Add milk; IF (sugar is required) THEN add sugar; ELSE do nothing; ENDIF; Serve; END.

57 Algorithm for making buttered toast (No variable) Begin <ProgramButteredToast> get a loaf of bread. cut slice from the loaf of bread. move the slice of bread to the toaster. turn on the toaster. wait for the toaster to finish. move the slice of toast to a plate. spread the slice of toast with butter. turn off the toaster. End.

58 Algorithm for making buttered toast (with variables) LET A = a loaf of bread LET T = a toaster LET P = a plate LET B = some butter LET S = cut slice from A Begin <ProgramButteredToast> get A; move the S to T; turn on T; wait for T; move the S to P; spread S with B; End

59 Example using the curly braces { }

60 Ex. 1 Write Pseudocode algorithm to for a developer to create a mobile app that alerts you on your daily iternary on Campus. Use Sequence and Selection structures in your algorithm Ex. 1 Write Pseudocode algorithm showing your social media friend from America who is visiting you for the first time at the Legon Campus in Ghana. Your algorithm will be implemented on the google GIS so that he will not call you on phone. Unfortunately, you are writing an exams at the same time he touches the ground at Kotoka Airport. Logically direct him on pick and drop vehicle points, up to your hall room 10. Use Sequence and Selection structures in your algorithm

61 Thank you