Introduction to Flowcharting

Size: px

Start display at page:

Download "Introduction to Flowcharting"

Cory Wilkinson
6 years ago
Views:

1 Introduction to Flowcharting 1

2 Acknowledgment This tutorial is based upon Appendix C from Starting Out with C++: From Control Structures to Objects (5th Edition) Copyright Tony Gaddis 2007 Published by Addison-Wesley 2

3 Definitions A flowchart depicts pictorially the sequence in which instructions are carried out in an algorithm. A flowchart is a schematic representation of an algorithm or a stepwise process, showing the steps of boxes of various kinds and their order by connecting these with arrows. Flowcharts are used not only as aids in developing algorithms but also to document algorithms. Flowcharts are used in designing or documenting a process or program.

4 Need for the flowchart Efficient Communication Efficient Analysis Proper Documentation Easy and efficient coding Program Debugging Program Maintenance

5 What is a Flowchart? A flowchart is a diagram that depicts the flow of control of a program. START Display message How many hours did you work? Read Hours Display message How much do you get paid per hour? Read PayRate Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 5

6 Basic Flowchart Symbols START Display message How many hours did you work? Rounded Rectangle Notice there are three types of symbols in this flowchart: rounded rectangles parallelograms a rectangle Each symbol represents a different type of operation. Rectangle Rounded Rectangle Read Hours Display message How much do you get paid per hour? Read PayRate Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END Parallelogram 6

7 Basic Flowchart Symbols Terminals represented by rounded rectangles indicate a starting or ending point START Display message How many hours did you work? Read Hours Display message How much do you get paid per hour? Read PayRate Terminal START Multiply Hours by PayRate. Store result in GrossPay. END Terminal Display GrossPay END 7

8 Basic Flowchart Symbols Input/Output Operations represented by parallelograms indicate an input or output operation START Display message How many hours did you work? Read Hours Display message How much do you get paid per hour? Read PayRate Input/Output Operation Display message How many hours did you work? Read Hours Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 8

9 Basic Flowchart Symbols Processes represented by rectangles indicates a process such as a mathematical computation or variable assignment Multiply Hours by PayRate. Store result in GrossPay. Process START Display message How many hours did you work? Read Hours Display message How much do you get paid per hour? Read PayRate Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 9

10 Stepping Through the Flowchart In the next seven slides we will step through each symbol in the flowchart. We will show the program output and the contents of the variables. START Display message How many hours did you work? Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours:? PayRate:? GrossPay:? Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 10

11 Stepping Through the Flowchart START Display message How many hours did you work? Step 1: An Output Operation How many hours did you work? Screen Output Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours:? PayRate:? GrossPay:? Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 11

12 Stepping Through the Flowchart START Display message How many hours did you work? How many hours did you work? 40 Step 2: An Input Operation (User types 40) Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours: 40 PayRate:? GrossPay:? The value 40 is stored in Hours. Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 12

13 Stepping Through the Flowchart START Display message How many hours did you work? How much do you get paid per hour? Screen Output Step 3: An Output Operation Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours: 40 PayRate:? GrossPay:? Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 13

14 Stepping Through the Flowchart START Display message How many hours did you work? How much do you get paid per hour? 20 Read Hours Display message How much do you get paid per hour? Step 4: Input Operation Read PayRate Variable Contents: Hours: 40 PayRate: 20 GrossPay:? (User types 20) The value 20 is stored in PayRate. Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 14

15 Stepping Through the Flowchart START Display message How many hours did you work? How much do you get paid per hour? 20 Step 5: The product of Hours times PayRate is stored in GrossPay Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours: 40 PayRate: 20 GrossPay: 800 The value 800 is stored in GrossPay. Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 15

16 Stepping Through the Flowchart START Display message How many hours did you work? Your gross pay is 800 Screen Output Read Hours Display message How much do you get paid per hour? Read PayRate Variable Contents: Hours: 40 PayRate: 20 GrossPay: 800 Step 6: An Output Operation Multiply Hours by PayRate. Store result in GrossPay. Display GrossPay END 16

17 Four Flowchart Structures Sequence Decision (Selection) Repetition (Iteration) Case

18 Sequence Structure A series of actions are performed in sequence The pay-calculating example was a sequence flowchart. 18

19 Selection Structure One of two possible actions is taken, depending on a condition. 19

20 Selection Structure A new symbol, the diamond, indicates a yes/no question. If the answer to the question is yes, the flow follows one path. If the answer is no, the flow follows another path NO YES 20

21 Selection Structure In the flowchart segment below, the question is x < y? is asked. If the answer is no, then process A is performed. If the answer is yes, then process B is performed. NO x < y? YES Process A Process B 21

22 Selection Structure The flowchart segment below shows how a decision structure is expressed in C as an if/else statement. Flowchart C Code NO x < y? YES if (x < y) a = x * 2; else Calculate a as x plus y. Calculate a as x times 2. a = x + y; 22

23 Selection Structure The flowchart segment below shows a decision structure with only one action to perform. It is expressed as an if statement in C code. Flowchart C Code NO x < y? YES if (x < y) a = x * 2; Calculate a as x times 2. 23

24 Iteration Structure An iteration structure represents part of the program that repeats. This type of structure is commonly known as a loop. 24

25 Iteration Structure Notice the use of the diamond symbol. A loop tests a condition, and if the condition exists, it performs an action. Then it tests the condition again. If the condition still exists, the action is repeated. This continues until the condition no longer exists. 25

26 Iteration Structure In the flowchart segment, the question is x < y? is asked. If the answer is yes, then Process A is performed. The question is x < y? is asked again. Process A is repeated as long as x is less than y. When x is no longer less than y, the iteration stops and the structure is exited. x < y? YES Process A 26

27 Iteration Structure The flowchart segment below shows an iteration structure expressed in C as a while loop. Flowchart C Code while (x < y) x < y? YES Add 1 to x x++; 27

28 Controlling an Iteration Structure The action performed by an iteration structure must eventually cause the loop to terminate. Otherwise, an infinite loop is created. In this flowchart segment, x is never changed. Once the loop starts, it will never end. QUESTION: How can this flowchart be modified so it is no longer an infinite loop? x < y? YES Display x 28

29 Controlling an Iteration Structure ANSWER: By adding an action within the iteration that changes the value of x. YES x < y? Display x Add 1 to x 29

30 A Pre-Test Iteration Structure This type of structure is known as a pre-test iteration structure. The condition is tested BEFORE any actions are performed. YES x < y? Display x Add 1 to x 30

31 A Pre-Test Iteration Structure In a pre-test iteration structure, if the condition does not exist, the loop will never begin. YES x < y? Display x Add 1 to x 31

32 A Post-Test Iteration Structure This flowchart segment shows a post-test iteration structure. The condition is tested AFTER the actions are performed. A post-test iteration structure always performs its actions at least once. Display x Add 1 to x x < y? YES 32

33 A Post-Test Iteration Structure The flowchart segment below shows a post-test iteration structure expressed in C as a do-while loop. Flowchart Display x Add 1 to x C Code do { printf( %d,x); x++; } while (x < y); x < y? YES 33

34 Case Structure One of several possible actions is taken, depending on the contents of a variable.

35 Case Structure The structure below indicates actions to perform depending on the value in years_employed. CASE years_employed Other bonus = 100 bonus = 200 bonus = 400 bonus = 800

36 Case Structure If years_employed = 1, bonus is set to 100 If years_employed = 2, bonus is set to 200 CASE years_employed If years_employed = 3, bonus is set to 400 If years_employed is any other value, bonus is set to Other bonus = 100 bonus = 200 bonus = 400 bonus = 800

37 Connectors Sometimes a flowchart will not fit on one page. A connector (represented by a small circle) allows you to connect two flowchart segments. A 37

38 Connectors The A connector indicates that the second flowchart segment begins where the first segment ends. START A A END 38

39 Modules A program module, such as a subprogram (or function in C), is represented by a special symbol. 39

40 Modules The position of the module symbol indicates the point the module is executed. A separate flowchart can be constructed for the module. START Read Input. Call calc_pay function. Display results. END 40

41 Combining Structures Structures are commonly combined to create more complex algorithms. The flowchart segment below combines a selection structure with a sequence structure. YES x < y? Display x Add 1 to x 41

42 Combining Structures This flowchart segment shows two selection structures combined. NO x > min? YES Display x is outside the limits. NO x < max? YES Display x is outside the limits. Display x is within limits. 42

43 Review What do each of the following symbols represent? (Answer on next slide)

44 Answer What do each of the following symbols represent? Terminal Decision Input/Output Operation Connector Process Module

45 Review Name the four flowchart structures. (Answer on next slide)

46 Answer Sequence Decision Repetition Case

47 Review What type of structure is this? (Answer on next slide)

48 Repetition Answer

49 Review What type of structure is this? (Answer on next slide)

50 Sequence Answer

51 Review What type of structure is this? (Answer on next slide)

52 Case Answer

53 Review What type of structure is this? (Answer on next slide)

54 Decision Answer

depicts pictorially schematic representation of an algorithm document algorithms. used in designing or documenting

depicts pictorially schematic representation of an algorithm document algorithms. used in designing or documenting Definition A flowchart depicts pictorially the sequence in which instructions are carried out in an algorithm. A flowchart is a schematic representation of an algorithm or a stepwise process, showing the