Procedures cont and Loops

1
Procedures (cont) and Loops

• CS0004
• Chapter 4, 6.1, and 6.3

2
Administration

• Graded First Part of Project
• Get them after class
• Will review design
• Extended Final Project Deadline
• Until next Wednesday (Feb 7th)
• Will send email about submitting project
• Questions?

3
Project 1 (interface)
ListBox
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Project 1 (psuedocode)

• NOTE 1 Rock 2 Paper 3 Scissors
• Event Rock_Click
• Clear items in lstOutput
• Output "Player choice Rock" to lstOutput
• choice Generate random number between 1 and
  3 If (choice 1) Then
• Output "Computer choice Rock" to lstOutput
• Output "TIE GAME!" to list box
• ElseIf (choice 2) Then
• Output "Computer choice Paper" to lstOutput
• Output "COMPUTER WON!" to lstOutput
• Else
• Output "Computer choice Scissors" to
  lstOutput
• Output "PLAYER WON!" to lstOutput
• End If
• Output "Click any button to play again!"

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Project 1 (psuedocode)

• Need to define it for other events
• Paper Button Click
• Scissors Button Click
• Should follow from the rock button click

6
Review

• What are parameters?
• What is the difference between ByVal and ByRef?
• What is the difference between a sub-procedure
  and a function?
• Why do we have procedures and functions?

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Modular Design

• Save on typing
• Break big tasks into small procedures and
  functions
• Keep from making errors (easy to test)
• Examples?

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Lets try it out

• Design a program to convert Fahrenheit to Celsius
• Use a function to compute the conversion
• Use a sub procedure to display the result

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Loops

• Many, Many times you want to repeat the same
  piece of code over and over again
• We observed this with procedures already
• Three Types of Loops
• Do While
• Do Until
• For Next

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Do While

• This allows you to loop until some conditional
  statement becomes false
• Do While Condition
• CODE BLOCK
• Loop
• Executes until Condition is false
• Checks Condition at beginning of loop

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Do While (example)

• Display the number 1 to 7 in a list box
• Dim num As Integer 1
• Do While num lt 7
• lstNumbers.Items.Add(num)
• num 1
• Loop

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Do While
Is the condition True?
No
Yes
Execute Code in Loop
Execute Code After the Loop
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Do Until

• This allows you to execute some code and continue
  to execute over and over until a condition is
  true
• Do
• CODE BLOCK
• Loop Until Condition
• This executes until condition is True
• Does not check condition before entering loop

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Do Until (example)

• Display the number 1 to 7 in a list box
• Dim num As Integer 1
• Do
• lstNumber.Items.Add(num)
• num 1
• Loop Until num gt 7

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Do Until
Execute Code in Loop
Is the condition True?
No
Yes
Execute Code After the Loop
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Nested Loops

• Just like if statements we can nest loop
• Do While cond1
• Do While cond2
• block1
• Loop
• Loop

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For Loops

• Many times you loop a specified number of times
  (as in examples)
• Counting with Counters
• Dim num As Integer 1
• Do While num lt 7
• Stuff
• num 1
• Loop
• There is a better way called For Loops

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For Loop

• For loops automatically count for us
• For num 1 to 7
• Stuff
• Next
• No need to count ourselves
• Stops with num gt 7

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Step Values

• Dont necessarily have to count by 1
• For num 0 To 10 Step 2
• stuff
• Next
• This counts by 2
• Will count 0,2,4,6,8,10

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Negative Steps

• What if we want to count backwards
• Use a negative step
• For num 10 To 1 Step -1
• stuff
• Next
• Will stop when num gt 1
• 10,9,8,7,6,5,4,3,2,1

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Control Variable

• In For loops the counter variable is also known
  as the control variable
• For num 1 to 7
• Stuff
• Next
• Do NOT modify this variable in the loop
• Could loop forever
• Unpredictable behavior

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Forever Loops

• This is when the loop never stops
• Dim num As Integer 1
• Do While num lt 7
• lstNumbers.Items.Add(num)
• Loop
• This will never stop
• Need to be careful
• Called Infinite Loop

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Example

• Lets try it out, display a group of numbers
  between two points given a step value