1. Unit 6 - Subroutines

2. Structured Programming
Main Topics
Structured Programming
Subroutines
Parameter Passing with Subroutines
Control Structures and Subroutines
Problem Solving with Structured Programming

3. What we will be doing this chapter
Organizing Programs by breaking them up into “mini” programs
Writing our own functions! (like Len, Asc, Chr, etc from last unit!)

4. I can…
Define and describe structured programming and its purpose.

5. Why is Structured Programming Needed???
Look back at the past….
Programming in older versions of BASIC vs. Modern Styles of Programming
“Spaghetti Code”:
Hopelessly intertwined statements caused by numerous “jumps” between sections of code
Nearly impossible to follow – would just between lines – no flow

6. What is Structured Programming??
Dividing a program into a hierarchy of modules or subprograms
Large complicated problems are broken into smaller, easier to manage problems
“Divide and Conquer” Method
Example: Planning a Party

7. What is structured programming??
Program is broken up into modules
Mini subproblems/sub routines
Each subroutine includes its own:
Purpose
Declaration
Statements
Each acts like a separate mini program – but when all put together solve a bigger problem!

8. What is Structured Programming
Modular Programming  another name for structured programming
Programming in this style then becomes about putting together the modules (mini programs) in a productive way.
Ex: Finding the area of a Trapezoid

9. How to Write a Structured (Modular) Program
Top- Down Design
Breaking a large programming task (the “Top”) into smaller and smaller subtasks (the “Bottom”)
Subprograms are implemented (written) by Subroutines
Subroutines are accessed (used) by Call Statements
Subroutines are called from the Main Program

10. Process of Top-Down Design
First – identify the major tasks to be performed.
Put in outline form – this outline becomes the basis of the main program
Avoid thinking about details of how to implement the individual subprograms – but instead focus on the “Top” big picture
Write the main program as a series of remarks (comments) and subroutine calles based on the outline of the major tasks

11. Then Work Down!!
After you have the outline complete – then work down to fill in the details!!!!
Each subroutine performs ONE of the major tasks – thus it has a VERY limited purpose
This is where you deal with the details!

12. Advantages of Top-Down Structured Programming
Programs will be easier to read!
Will be full of documentation as each subprogram explains its purpose and function!
Programs will be easier to write!
Complicated problems broke down into smaller easier to manage subproblems
Only after main tasks identified do you worry about the details.
Programs are easier to use, change, adapt, modify, and debug

13. Advantages of Top-Down Structured Programming
Programs are easier to reuse
A module that performs a specific task can be
Copied into another program needing the same task
Can be reused in the same program by calling it multiple times.
Other, more powerful programming languages require this kind of structure

14. Steps of Top-Down Structure Programming
Start with an outline of the main program
Write down English phrases to list and describe the major tasks to be performed
AVOID thinking about the details of each major task
Code the main program
Translate each English phrase into one or two Visual Basic subroutine calls
Use plenty of documentation to describe the actions and make the program more readable.

15. Steps of Top-Down Structure Programming
Program the details by writing each subroutine.
Open the form’s code window
Define the Subroutine
Give the Function a meaningful name!
Select the type – “Sub”
Select the Scope Type – normally “Private”
Then type your code for that subroutine

16. Basics of Subroutine will ApPear in Code
<Private or Public> Sub <name>() ... … End Sub

17. Steps of Top-Down Structure Programming
Test the completed program
Use a complete set of test data to be sure it works
Makes any changes or refinements that are necessary or desireable

18. Homework
Read Handout and Answer Corresponding Questions

20. Subroutines!!!
I can write subroutines (mini programs) for a program with Structured Programming!

21. Structured Programming
Dividing a program into hierarchy of modules or subprograms
Large, complicated programs are broken into smaller, easier to manage subproblems
Subprograms are implemented by Subroutines
Subroutines are accessed by Call statements
Subroutines are called from the Main Program

22. Subroutines One of Visual Basic’s ways of writing subprograms
Two parts to a subroutine
Subroutine Call (found in the main program)
Subroutine Implementations (where written)

23. Subroutine IMplementation
The actual CODE for the subproblem
Note: Each time we write code for a button – we are writing a subroutine – “call” happens when button clicked!
Syntax
Private Sub <subroutine name>(<parameter list>) …
End Sub

24. Subroutine Names MUST start with a letter
Can contain letters, numbers, underscores
Cannot be a reserved word (TextBox, Integer, etc)

25. Parameters Private Sub <subroutine name>(<parameter list>)
Syntax
Private Sub <subroutine name>(<parameter list>) …
End Sub
Parameter List is OPTIONAL – contains variables they are to be used within the subroutine!

26. Creating a Subroutine Open the Form’s code Window (View  Code)
Define the Subroutine
Give the function a meaningful name
Select type “Sub”
Select scope – generally “Private”
Then type the code for that subroutine part in the code window!

27. Subroutine Call
The code used in the MAIN PROGRAM to access the subroutine!
Syntax
Call <subroutine name>(<parameter list>)
Examples
Call FindAverage(x, y)
Call PrintOutput()

28. Unit6Ex1 Create an Example entitled Unit6Ex1
Add a Label with the words “Structured Programming Example”
Add a ListBox!  Stretch it out to make it wider!
Create a Common Button with the words “Start”
Double Click the Button

29. Unit6Ex1
Private Sub.... ‘ Call the first subroutine Call First() ‘ Call the second subroutine Call Second() ‘ Call the third subroutine Call Third() ‘ Call the fourth subroutine Call Fourth() End Sub

30. Name: First Type: Sub Scope: Private
Creating Subroutines
Stay in the Coding Menu. After “End Sub” we are going to start our own, new subroutine.
Name: First Type: Sub Scope: Private
Private Sub First()
ListBox1.Items.Add(“This is the first subroutine”)
End Sub

31. Subroutines 2, 3, and 4 Similar!
Private Sub Second() ListBox1.Items.Add(“This is the second subroutine”) End Sub Private Sub Third() ListBox1.Items.Add(“This is the third subroutine”)

32. Subroutine 4!
Private Sub Fourth () ListBox1.Items.Add(“This is the fourth subroutine”) End Sub

33. Create Another Subroutine
Private Sub DividingLine()
ListBox1.Items.Add(“ ”)
End Sub

34. Alter our Main Program (Button)
Private Sub.... ‘ Call the first subroutine Call First() ‘ Draw a Dividing Line Call DividingLine() ‘ Call the second subroutine Call Second()

35. Alter Main Program
‘ Call the third subroutine Call Third() ‘ Draw a Dividing Line Call DividingLine() ‘ Call the fourth subroutine Call Fourth() End Sub

36. Your program should have the following output:
With a Partner!!
Start a New Project Entitled: Unit6Ex2
Write a program that contains THREE subroutines.
Prints your name
Prints your partner’s name
Prints a line of asterisks
Your program should have the following output:
****************************
First Person’s Name
Second Person’s Name

37. With a Partner!! Be sure to: Use a command button to start the program
Write your main program within this command button
Use comments within the main program describing the actions

38. Homework
Worksheet 6A

40. Parameter Passing with Subroutines
Today we’ll be adding in PARAMETER Passing
We used parameters with our functions last chapter  we had to send in a “parameter” and the function did something with that parameter!
Len  used a string
Mid  used a string, starting integer, and number of integers

41. Recall
Structured Programming – dividing a program into a hierarchy of modules/subprograms
Subroutines:
One of Visual Basic’s ways of writing subroutines
Two parts:
Subroutine Call (main program)
Subroutine Implementation (code written separate from the main program)
Each subroutine acts like its own program (own variables, input, If..Then.., loops, etc)

42. Problem
If each subroutine is it’s own program, how is information shared between the different subprograms???
How do I get data that is help within one subroutine into another one for processing???
Answer: Parameters!!

43. Subroutines using a Parameter
Subroutine Call Syntax
Call <subroutine name> (<parameter list>)
Subroutine Implementation Syntax
Private Sub <subroutine name> (<parameter list>)

44. Parameter
The parameter provides a method of transferring data from the main function.
Ex: Len(word)  takes in a STRING that we send in!
Ex: Asc(“A”)  takes in a CHARACTER that we send in!
Ex: Chr(45)  takes in an INTEGER that we send in!

45. Two Ways to Write a Parameter List
ByVal  sends the VALUE in….the variable in the main program will not be changed.
Variables received from Main program declared in parameter statement of Subroutine!!
In Main Program
Dim x As Single
x = -48
Call PrintSquare(x)
ListBox1.Items.Add(x)
Subroutine
Private Sub PrintSquare(ByVal num As Single)
num = num * num
ListBox1.Items.Add(“The square is “ &
num)
End Sub

46. Subroutines Using parameters

47. Subroutines with parameters - ByVal
Steps:
The value of variable x from the main program is copied into the variable num in the subroutine
Variable num is manipulated and the variable x goes unchanged.

48. Two Ways to Write a Parameter List
ByRef  sends the reference (where located in memory)….the variable in the main program can changed.
In Main Program
Dim x As Single
x = -48
Call PrintSquare(x)
ListBox1.Items.Add(x)
Subroutine
Private Sub PrintSquare(ByRef num As Single)
num = num * num
ListBox1.Items.Add(“The square is “ &
num)
End Sub

49. Subroutines Using parameters

50. Subroutines with parameters - ByRef
Steps:
The reference (location) of x from the main program is copied into the variable num in the subroutine
Variable num are referencing the same location.
Both are manipulated and the x value will have the same value as num after the subroutine has run.

51. Example 1: In Main Program Subroutine Dim x As Single
Call Print Square(x)
ListBox1.Items.Add(x)
ListBox1.Items.Add(num)
Subroutine
Private Sub PrintSquare(ByVal num As Single)
num = num * num
ListBox1.Items.Add(“The square is “ &
num)
End Sub
What if we tried to print out the variable from the subroutine?!? In the main?

52. What happens?? Num is NOT a variable of our main Program!!
As a result  it cannot be manipulated, printed, etc in our main program.
Since it is defined in our SUBROUTINE our SUBROUTINE is where it is used.
Does the same apply for the variables in our main program? Are they specific to the main program?!?

53. Example 2: In Main Program Dim x As Single x = -48
Call Print Square(x)
ListBox1.Items.Add(x)
Subroutine
Private Sub PrintSquare(num As Single)
num = num * num
ListBox1.Items.Add(“The square is “ &
num)
ListBox1.Items.Add(“x = “ & x)
End Sub
What if we tried to print out the variable from the main in the subroutine?!?

54. What happens?? x is NOT a variable of our subroutine!!
As a result  it cannot be manipulated, printed, etc in our subroutine.
Since it is defined in our Main program our Main Program is where it is used.

55. Sample Program: Finding the average of 3 numbers
Let’s think this our using our Structured Programming model first…How should be break down our “big problem”

56. Subroutine Break Down:
Our program will need 4 subroutines
Intro: Introduced and examples the program
EnterData: Allows the user to enter three numbers
Calc Average: Calculates the Average
OutputResults: Prints the three numbers and their average

57. Unit6ex3 Open a new form called Unit6Ex3
Create a Label and have it say: Average of Three Numbers
Add a Command Button and have it say: Start
Add a ListBox!

58. Code Window Think before you code!!
What variables will we need?? How many variables??
In what order will our subroutines be called??
Write down in English BEFORE coding!

59. Unit6Ex3
Private Sub Button….. Dim a As Single ‘ first number Dim b As Single ‘ second number Dim c As Single ‘ third number Dim average As Single ‘ average of three numbers ‘ Program Introduction Call Intro()

60. UniT6ex3
‘ Input Data Call EnterData(a, b, c) ‘ Find the Average Call CalcAverage(a, b, c, average) ‘ Output the results Call OutputResults(a, b, c, average) End Sub

61. First Subroutine: Intro
Now we can think about the specifics of each
What do we want the intro subroutine to do?
Are any variables needed? If so…what??

62. First Subroutine: Intro
Private Sub Intro() ListBox1.Items.Add(“Welcome to the Averaging Program”) ListBox1.Items.Add(“I find the average of 3 numbers!”) ListBox1.Items.Add(“Let’s get started!”) End Sub

63. Second Subroutine –EnterData
What is the purpose of the second subroutine?
Are any variables needed to be modified here??
What will our parameters be?

64. Second Subroutine – EnterData
Private Sub EnterData(ByRef a As Single, ByRef b As Single, ByRef c As Single) a = InputBox(“Enter the first value”, “Input a”) b = InputBox(“Enter the second value”, “Input b”) c = InputBox(“Enter the third value”, “Input c”) End Sub **Use ByRef because all variables sent in will need to be changed!!**

65. Third Subroutine – Calculate the Average
What is the purpose of the third subroutine?
Are any variables needed to be modified here??
What will our parameters be?

66. Third Subroutine – Calculate the Average
Private Sub CalcAverage(ByVal a As Single, ByVal b As Single, ByVal c As Single, ByRef average as Single)
average = (a + b + c) / 3
End Sub
**Use ByRef 0nly for average…because that is the only variable from the main program we want changed!!**

67. Fourth Subroutine – output Results
What is the purpose of the third subroutine?
Are any variables needed to be modified here??
What will our parameters be?

68. Fourth Subroutine – output Results
Private Sub OutputResults(ByVal a As Single, ByValb As Single, ByVal c As Single, ByVal average as Single)
ListBox1.Items.Add(“Three Values Entered: ” & a & “, “ & b &
“, “ & c)
ListBox1.Items.Add(“Average: “ & average)
End Sub
**Use ByVal for all  no values sent in must in changed in main prog**

70. With a Partner: Trapezoid Area
Recall we wrote a program at the beginning of the semester that found the area of a trapezoid!
A = ½ h(b1 + b2)
Rewrite this program using the four subroutines with parameters!
Program Introduction
Inputs height and lengths of the bases
Calculate the area of the trapezoid
Outputs the area in a textbox
Recall: Use a button to start the program (main code) and use comments to describe the actions.

71. With a Partner: Slope of Line
Recall we wrote a program at the beginning of the semester that found the slope of a line!
Rewrite this program using the three subroutines with parameters!
Inputs coordinates of the two points
If x1 = x2…calculates the slope
Outputs the slope or tells if the slope is undefined
Recall: Use a button to start the program (main code) and use comments to describe the actions.

72. With a Partner: Trapezoid Area
Recall we wrote a program at the beginning of the semester that found the area of a trapezoid!
A = ½ h(b1 + b2)
Rewrite this program using the four subroutines with parameters!
Program Introduction
Inputs height and lengths of the bases
Calculate the area of the trapezoid
Outputs the area in a textbox
Recall: Use a button to start the program (main code) and use comments to describe the actions.

73. With a Partner: Slope of Line
Recall we wrote a program at the beginning of the semester that found the slope of a line!
Rewrite this program using the three subroutines with parameters!
Inputs coordinates of the two points
If x1 = x2…calculates the slope
Outputs the slope or tells if the slope is undefined
Recall: Use a button to start the program (main code) and use comments to describe the actions.

74. With a Partner: Trapezoid Area
Recall we wrote a program at the beginning of the semester that found the area of a trapezoid!
A = ½ h(b1 + b2)
Rewrite this program using the four subroutines with parameters!
Program Introduction
Inputs height and lengths of the bases
Calculate the area of the trapezoid
Outputs the area in a textbox
Recall: Use a button to start the program (main code) and use comments to describe the actions.

75. With a Partner: Slope of Line
Recall we wrote a program at the beginning of the semester that found the slope of a line!
Rewrite this program using the three subroutines with parameters!
Inputs coordinates of the two points
If x1 = x2…calculates the slope
Outputs the slope or tells if the slope is undefined
Recall: Use a button to start the program (main code) and use comments to describe the actions.

77. Review of Structured Programming and Subroutines
What would the output of the program in front of you be.

78. Review What is Structured Programming?
Name give advantages to Structured Programming
What are the steps of Structured Programming?

79. What is Structured Programming?
Review
What is Structured Programming?
Dividing a program into a hierarchy of modules or subprograms

80. Name give advantages to Structured Programming
Review
Name give advantages to Structured Programming
Programs will be easier to read
Programs will be easier to write.
Programs will be easier to use, changes, adapt, modify, and debug
Programs are easier to reuse
Other more power programming languages require this structure

81. What are the steps of Structured Programming?
Review
What are the steps of Structured Programming?
Start with an outline of the main program
Code the main program
Program the details by writing each subroutine
Test the completed program

83. Control Structures, Subroutines, and Structured Programming
I can describe methods for which the transfer of control is accomplished within a Visual Basic program.

84. Recall:
Structured Programming – dividing a program into a hierarchy of modules/subprograms
Subroutines:
One of Visual Basic’s ways of writing subroutines
Two parts:
Subroutine Call (main program)
Subroutine Implementation (code written separate from the main program)
Each subroutine acts like its own program (own variables, input, If..Then.., loops, etc)

85. Recall:
Control structures: Methods in which transfer of control (the order in which program statements are performed) is accomplished
Three types
Sequential (Linear)
Selection (Branching/Decision)
Iteration (Repetition/Looping)
Often Represented using FLOWCHARTS (shows the flow of control!)

86. Control Structures
Sequential (Linear)  ONE flow **What all the programs we have done so far have looked like**

87. Control Structures Single selection: If…Then
Selection (Decision)  Split at Decisions - multiple paths
Single selection: If…Then
Double selection: If…Then…Else
Multiple-selection: If…Then…ElseIf
Select Case

88. Control Structures
Repetition (Looping) repeat code numerous times Fixed repetition: For…Next Variable repetition: While Do While Do Unit Do Loop…While Do Loop…Until

89. Why Needed?
Control Structures allowed us to create programs that followed a LOGICAL sequence
Using forbidden control blocks that cause jumps (GoTo code) disrupts that logical sequence and flow of the program
Remove the structure!

90. Control Structures and Subroutines
When writing programs you need to consider….
The major tasks to be performed (determines subroutines!!)
The actions involved in each major task (type of control structure to use!)

91. Structures Problem Solving with Top-Down Programming
4 things happen BEFORE we code the program!!
Problem Definition
What am I being asked to do?
Write a brief description of the purpose of the program and what it is to accomplish
Input/Output Format Specification
What information will the program need to be given while executing
What information will the program need to be printing

92. Structures Problem Solving with Top-Down Programming
4 things happen BEFORE we code the program!!
Algorithm Design
Write an outline of the major tasks to be performed
Arrange this list into the order in which they are to be performed
Determine the control structures needed to perform each task
Data Structure Analysis
What types of variables (strings, singles, integers, etc) will be needed?
What will be the function (role) of each variable?
What meaningful names can be given to the variables?

93. Structures Problem Solving with Top-Down Programming
Coding the Program
Outline the main program from the algorithm
Code the main program as a series of call statements – including documentation for the variable list and description of the purpose of each Call statement
Code the Subroutines – design and write each subroutine in detail, paying attention to the type of control structures used in each

94. Structures Problem Solving with Top-Down Programming
2 things happen After we code the program!!
Testing the Program
Design a complete set of test data that will demonstrate that the program functions property for all possible data and in all possible cases
Does the program work ALL the time?? Does it crash when given “bad” input???

95. Structures Problem Solving with Top-Down Programming
2 things happen After we code the program!!
Evaluation, Modification, and Refinement
How can the program be improved?
How can the output be improved to make it more readable, descriptive, and visually appealing?
What features can be added to the program to make it a better, more useful, and more user friendly program?
What changes are necessary to make the program work in all possible cases?