1. PROGRAM DESIGN CONCEPTS AND TECHNIQUES
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Structured Programming: Unit 3 Slide 1

2. Objectives Use functions and subprocedures to modularize a program.
Divide a program into modules.
Use parameters and return values to pass data between modules.
Identify situations appropriate for using value parameters.
Identify situations appropriate for using reference parameters.
Choose the appropriate scope for a variable.
Create a function.
Use recursion to solve a programming problem.
Describe overall design goals and program requirements.
Use a data flow diagram to show how data flows between modules.
Use an IPO chart to show how data flows between modules.
Write algorithms and pseudocode to describe a program.
Use pseudocode to describe a subprogram that uses parameters.
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Structured Programming: Unit 3 Slide 2

3. Benefits of Using Modules
Reusing a module
Hiding code complexity
Allowing multiple programmers to work on a project
Ability to test at the module level
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Structured Programming: Unit 3 Slide 3

4. Data Flow Diagram Main module OriginalPrice DiscountRate OriginalPrice
Saleprice
Saleprice
Input data
Compute
results
Output data
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Structured Programming: Unit 3 Slide 4

5. IPO Chart Input Processing Output OriginalPrice DiscountRate
Compute SalePrice
SalePrice
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6. Parameters and Arguments
Call OutputResults (OriginalPrice, DiscountRate, SalePrice)
Subprogram OutputResults (OldPrice, Rate, NewPrice)
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Structured Programming: Unit 3 Slide 6

7. Value and Reference Parameters Example
Main
Set Num1 = 1
Set Num2 = 2
Call Switch(Num1, Num2)
Write Num1, “ “ , Num2
End Program
Subprogram Switch(Number1, Number2 As Ref)
Set Number1 = 2
Set Number2 = 1
End Subprogram
5/2/2019© 2006 ITT Educational Services Inc.
Structured Programming: Unit 3 Slide 7

8. Variable Scope Main DECLARE Num1 Num1 = 4 Call DoSomething()
Write Num1
Subprogram DoSomething()
Declare Num1
Declare Num2
Num1 = 3
Num2 = Num1 * 2
Write Num1, Num2
End Subprogram
Subprogram DoSomething2()
Declare Num2
Num2 = 2
Write Num1, Num2
End Subprogram
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Structured Programming: Unit 3 Slide 8

9. Variable Scope in VB.NET
Module Module1
Dim modLevelVar As Integer = 100
Sub Main()
Dim subLevelVar As Integer = 1
If subLevelVar = 1 Then
Dim strIfOnly As String = "within if only" System.Console.WriteLine(strIfOnly)
End If
System.Console.WriteLine(strIfOnly)
modLevelVar = subLevelVar
End Sub
End Module
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Structured Programming: Unit 3 Slide 9

10. Variable Scope in Java public class ScopeTest { static void mod1(x)
int i = 5*x;
System.out.println("value = " + i); }
public static void main(String[] args)
int x = 10;
int i = x+5; //Here i = 15
if x < i
int i = x; //Here i = 10
mod1(i);
mod1(i); //Here i still = 15
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Structured Programming: Unit 3 Slide 10

11. Functions Main Declare Num As Real Set Num = Cube(10) Write Num
End Program
Function Cube(X) As Real
Set Cube = X^3
End Function
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12. Recursion Function Power(X, N) As Real If N = 1 Then Set Power = X
Else
Set Power = Power(X, N-1) * X
End If
End Function
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Structured Programming: Unit 3 Slide 12

13. Hierarchy Chart for a Grade Management Program
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14. Data Flow Diagram for a Grade Management Program
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15. Grades Management Program Pseudocode - Main
Declare Choice As Integer
Display a welcome message
Repeat
Call SelectFromMenu(Choice)
If Choice = 1 Then
Call CreateGradeSheet
End If
If(Choice = 2 Or (Choice = 3) or Choice=4) then
Call RetrieveGradeSheet(Choice)
Until Choice = 0
End Program
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16. Grades Management Program Pseudocode - SelectFromMenu
Subprogram SelectFromMenu(Choice As Ref)
Repeat
Write “0-Quit the program”
Write “1-Create grade sheet”
Write “2- Enter test scores”
Write “3-Compute test averages”
Write “4-Display grade sheet”
Input Choice
Until (Choice=Int(Choice) And (Choice>=0) And (Choice<=4)
End Subprogram
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17. Grades Management Program Pseudocode - CreateGradeSheet
Subprogram CreateGradeSheet
Declare Name As String
Open “GRADES” For Output As DataFile
Write “Enter student name; enter * when done.”
Input Name
While Name<>”*”
Write DataFile, Name, 0,0,0,0
End While
Close DataFile
End Subprogram
5/2/2019© 2006 ITT Educational Services Inc.
Structured Programming: Unit 3 Slide 17

18. Grades Management Program Pseudocode - RetrieveGradeSheet
Subprogram RetrieveGradeSheet(Choice)
Open “GRADES” For Input AS DataFile
Declare Names[40], Averages[40], Scores[3,40]
Set Count=0
While Not EOF(DataFile)
Set Count=Count+1
Read DataFile, Names[Count], Scores[1, Count], Scores[2, Count], Scores[3, Count], Averages[Count]
End While
Select Case of Choice
Case 2:
Call EnterTestScores(Count, Names, Scores)
Case 3:
Call ComputeAverages(Count, Scores, Averages)
Case 4:
Call DisplayGradeSheet(Count, Names, Scores, Averages)
End Case
Close DataFile
End Subprogram
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Structured Programming: Unit 3 Slide 18

19. Grades Management Program Pseudocode - EnterTestScores
Subprogram EnterTestScores(Count, Names, Scores As Ref)
Declare TestNum, K As Integer
Repeat
Write “Enter the test number:”
Input TestNum
Until (TestNum=1) Or (TestNum=2) Or (TestNum=3)
Write “When a name is displayed, enter test score.”
For K=1 Step 1 To Count
Write Names[K]
Input Scores[TestNum, K]
End For
End Subprogram
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Structured Programming: Unit 3 Slide 19

20. Grades Management Program Pseudocode - ComputeAverages
Subprogram ComputeAverages(Count, Scores, Averages As Ref)
Declare Sum, K as Integer
For K=1 Step 1 To Count
Set Sum=Scores[1,K] + Scores[2,K] +Scores[3,K]
Set Averages[K] = Sum/3
End For
End Subprogram
5/2/2019© 2006 ITT Educational Services Inc.
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21. Grades Management Program Pseudocode - DisplayGradeSheet
Subprogram DisplayGradeSheet(Count, Names, Scores, Averages)
Declare K As Integer
For K=1 Step 1 To Count
Write Names[K], Scores[1,K], Scores[2,K], Scores[3,K], Averages[K]
End For
End Subprogram
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Structured Programming: Unit 3 Slide 21

22. Summary In this unit, students learned:
The benefits of dividing a program into modules.
The methods of designing a program, including:
Data flow
IPO
How to pass data between modules:
Parameters
Return values
How to determine variable scope
Global
Local
How to select the best scope for a variable
How to use recursion to solve a problem.
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Structured Programming: Unit 3 Slide 22