Chapter 1: Problem Solving Skills Introduction to Programming GENG 200

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1 Chapter 1: Problem Solving Skills Introduction to Programming GENG 200 Spring 2014, Prepared by Ali Abu Odeh 1

2 Table of Contents Fundamentals of Flowcharts 2 3 Flowchart with Conditions Flowchart with Looping Expected Chapter Duration: 3 classes. Part 1 will be covered at the beginning of the course. Part 2 will be covered at the beginning of chapter 4. Part 3 will be covered at the beginning of chapter 5. Spring

3 Part 1: Fundamentals of Flowcharts Spring

4 Fundamentals of Flowcharts A flowchart is a type of a graphical diagram that represents an algorithm or process, showing the steps as shapes of various kinds, and their order by connecting them with arrows. This diagrammatic representation illustrates a solution to a given problem. Process operations are represented in these shapes, and arrows; rather, they are implied by the sequencing of operations. Spring

5 Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields. writing a procedure or a computer program to perform a certain task requires the need to organize the procedure using step-by-step instructions. Spring

6 1.2 Flowchart standards and shapes» When you draw a flowchart you must use standard shapes to represent each step in the procedure.» You usually draw the flow from top to bottom or from left to right.» Arrows connect the shapes to define the direction of the flow.» To draw a flowchart, a paper can be used or Microsoft Visio or the flowchart tool in Microsoft Word. Spring

7 Shape Meaning Shape: Arrow Shape: Oval Job: (Flow direction) Job: (Begin, End) Shape: Rectangle Job: Task (Process) Shape: Parallelogram Job: (Input, Output) Shape: Diamond Job: (Decision, Condition) used for Branching or Repeating Shape: Circle Job: (Connector) Spring

8 Key Points to draw flowchart» Brainstorm the tasks and decisions made during a process, and write them down in order.» Then map these out in flow chart format using appropriate symbols for the start and end of a process, for actions to be taken and for decisions to be made.» Finally, challenge your flow chart to make sure that it's an accurate representation of the process, and that it represents the most efficient way of doing the job. Spring

9 Example 1: Design a flowchart to calculate the area of a parallelogram given by this equation: area = base*height The flowchart for this procedure is as follows: h b Spring

10 Solution 1: begin get base get height area = base*height Output area End Spring

11 Solution 2: begin get base and height area = base*height Output area End Spring

12 Example 2: Design a flowchart to calculate the area of an octagon given by this equation: Area = 8tan(π/8)r 2 The flowchart for this procedure is as follows: Spring

13 Solution 1: begin pi = 3.14 get r area = 8 * tan (pi/8)*r 2 Output area End Spring

14 Solution 2: begin get r area = 8 * tan (3.14/8)*r 2 Output area End Spring

15 Practice 1: Draw a flowchart that will calculate the area of a trapezoid. b1 h Trapezoid area = ½ * h * (b1+b2) b2 Spring

16 Part 2: Flowchart with Conditions Spring

17 Flowchart with Decisions (Conditions) In real life it is typical that you have to choose between two options based on a certain parameter. An example is to decide to go to school by car or on foot. False/No Is Distance > 1.0 km? Go on foot True/Yes Go by car Spring

18 The previous flowchart may also be drawn as shown. False/No Is Distance > 2.0 km? True/Yes Go on foot Go by car Spring

19 » Usually the test (decision) achieved by asking certain questions, in English language referred to YES/NO question.» In computer languages they known as Boolean expressions; where the expression must have only two possible answers TRUE/FALSE.» These types of decisions can be constructed using set of operations like (=, <,<=, >, >=) Spring

20 » For example the following questions are valid in constructing decisions; is 4 < 3? is C > c? is num1 = num2? is counter <= 10?» The program will take a set of actions (or will skip them) based on the answer to the question, which will cause the program to flow into one of two possible branches. Spring

21 Flowchart with IF-Then construct The IF... THEN is shown here and is also known as the NULL else, meaning, that there is no else part. False if Condition True Process Spring

22 Example 3: Assume that the sides of a polygon are a1, a2, b1, and b2. If a1 = a2, b1 = b2, and a1 b1 then this polygon is a rectangle. Draw or design a flowchart to solve the problem. a1 b1 b2 a2 Spring

23 begin get a1,a2,b1,b2 is a1 = a2 and b1 = b2 and a1 b1 True / Yes False / No output "Polygon is rectangle" end Spring

24 The condition can be written in these way s: is a1 == a2 and b1 == b2 and a1!= b1 is a1 == a2 && b1 == b2 && a1!= b1 Spring

25 Flowchart with If-Else Construct A second variation of Decisions executes one block if the decision is true and another block if the decision is false. The only difference is that each value of the decision has a process associated with it. False if Condition True Process 2 Process 1 Spring

26 Example 4: Let s reconsider example 3 again, this time if the condition is false, then, the polygon is a square. Note: Yes means True and No means False. Spring

27 begin get a1,a2,b1,b2 is a1 = a2 and b1 = b2 and a1 b1 true false output "Polygon is square" output "Polygon is rectangle" end Spring

28 Flowchart with nested decisions A third variation of the decisional flowcharts uses several decisions (some time referred to as nested decisions), this construct at least has two decisions inside each other, if the result of the first test question is FALSE then the second question is tested.etc. until one test question evaluates to TRUE. Spring

29 False IF Condition 1 TRUE False IF Condition 2 TRUE PROCESS 1 IF Condition 3 TRUE PROCESS 2 False PROCESS 3 PROCESS 4 Spring

30 Example 5: Let s reconsider example 3 again, this time, you need to have a new branch if the polygon is not rectangle or square.» Nested if must be used here. Spring

31 begin get a1,a2,b1,b2 False is a1 = a2 and b1 = b2 and a1 b1 True is a1 = a2 and b1 = b2 and a1 = b1 output "Polygon is unidentified" True output "Polygon is square" output "Polygon is rectangle" End 31 Spring

32 Practice 2: Draw a flowchart for simulating a college grading system. <60 (F) <65 (D) <70 (D+) <75 (C) <80 (C+) <85 (B) <90 (B+) >=90 (A) Spring

33 Which one is more faster and more efficient? x_type = unknown x = -15 x_type = unknown x = -15 if x > 0 F T x_type = P if x > 0 T F x_type = P if x < 0 T if x < 0 T F x_type = N F x_type = N if x = 0 F T x_type = 0 if x = 0 F T x_type = 0 Spring

34 Practice 3: What is the output? x_type = unknown x = -15 x_type = unknown x = -15 if x > 0 F T x_type = P if x > 0 F T x_type = P if x < 0 T if x < 0 T F x_type = N F x_type = N if x = 0 F T x_type = 0 if x = 0 F T x_type = 0 Spring

35 Part 3: Flowchart with Looping Spring

36 Flowchart with Looping Conditional loops or repetitive control structures are a way for computer programs to repeat one or more various steps depending on conditions set either by the programmer initially or real-time by the actual program. A conditional loop has the potential to become an infinite loop when nothing in the loop's body can affect the outcome of the loop's conditional statement. Spring

37 Generally, the following classification is said to be universal for all looping constructs:» Counter control loops: This construct is used when the number (count) of repetitions (iterations) is known.» Sentinel value loops: This construct is used when the number of repetitions depends on certain value, which might be generated within the loop body or entered by the user. Spring

38 While loop While means (as long as) therefore, looping continues as long as the answer to the test question/condition is True. False Test Condition True PROCESS Spring

39 Example 6: Draw a flowchart that calculates and outputs the sum of the shown series. Ignore all elements whose values are less than y sin x sin x sin x sin x, x 0. 1 Spring

40 y sin x sin x sin x sin x, x 0. 1 x = 0.1 power = 1 z = 0 y = 0 x power z y z = sin (x ^ power) power = power Is z > ? True y = y + z False Spring

41 For loop You can see that there are three parts needed to draw a loop with a counter (termed as for loop):» Initialization of the counter.» Testing of the loop condition against the total count value.» Incrementing the counter each time the loop is executed. Spring

42 Generally, for loops are used when you know in advance the number of iterations. Initialize control variable False Condition (Test control variable) True Process Update control variable Spring

43 Example 7: What is the value of x after leaving the loop for both of them? counter = 0 x = 0 counter = 0 x = 0 counter = counter + 1 x = x + 2 counter = counter + 1 Is counter < 3? False True x = x + 2 Is counter < 3? False True Spring

44 Practice 4: Draw a flowchart that calculates and prints the average of several integers. Assume the last value read is the sentinel A typical input sequence might be indicating that the average of all the values preceding 9999 is to be calculated Spring

45 While or for? Generally, you can use while or for to solve any looping problem however, if you know how many times this loop will keep repeating in advance then, its better to use a for loop otherwise, better to use a while loop. Spring

References: - Slides, ERU team of instructors. - http://en.wikipedia.

46 References: - Slides, ERU team of instructors Spring

Problem Solving FLOWCHART. by Noor Azida Binti Sahabudin Faculty of Computer Systems & Software Engineering

Problem Solving FLOWCHART. by Noor Azida Binti Sahabudin Faculty of Computer Systems & Software Engineering Problem Solving FLOWCHART by Noor Azida Binti Sahabudin Faculty of Computer Systems & Software Engineering azida@ump.edu.my OER Problem Solving by Noor Azida Binti Sahabudin work is under licensed Creative