CS105 Lab 12 – Do-While-Loops

Announcements MP6 has been released and is due on

Tuesday, April 28th. Quiz 5 is now available and is due on

Tuesday, April 21st. Midterm 2 feedback sheets will be handed

out today in lab. Our final exam is on Monday, May 11th.

CS 105 – Spring 2009 1

Objectives

Develop a more sophisticated paint program

Nested-For-Loop Do-Until-Loop Generate a random number

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What we will do

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Last week, we: Painted

Horizontally/Right Vertically/Down Diagonally/Right

Changed the Brush Size

This week, we will do Paint Up and Left Paint a Square Paint a line until it

hits something Paint with random

color and length

For intOffset = 0 To mintBrushSize – 1Cells(intRow + intOffset, intCol).Interior.Color = vbBlue

Next intOffset

Last week

REMEMBER: We used a For-Loop to paint a line

How do we draw a line downward?

How do we draw a line rightward?

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For intOffset = 0 To mintBrushSize – 1Cells(intRow, intCol + intOffset).Interior.Color = vbBlue

Next intOffset

“+intOffset” ?“+intOffset” ?

REMEMBER: What we call an IF inside an IF? In a similar way, we call a For-Loop inside a

For-Loop a Nested-For-Loop

Paint a square

To paint a 5x5 square, we need to draw 5 lines, each containing 5 cells

We need a For-Loop to paint lines 1 through 5: AND for each line, we need another

For-Loop to draw 5 cells

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Nested-If

Paint a square

For intRowOffset = 0 To 4 For intColOffset = 0 To 4 Cells(intRow + intRowOffset, intCol + _

intColOffset).Interior.Color = vbBlue Next intColOffsetNext intRowOffset

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Dim intRowOffset As IntegerDim intColOffset As Integer

Tip: to observe the nested For-Loop stepby step you can call the “Delay” sub here

Paint a square, with the ActiveCell in the center

For intRowOffset = -2 To 2For intColOffset = -2 To 2

Cells(intRow + intRowOffset, intCol + _ intColOffset).Interior.Color = vbBlue

Next intColOffsetNext intRowOffset

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The previous code painted a square to the right and bottom of the ActiveCell. How can we draw it around the ActiveCell?

Paint until it hits a blue cell.

We want to paint a line from thethe ActiveCell, until it hits anothercell that is painted blue.

How do we do this? We don’t know how many cells we have to paint.

Therefore we cannot use a For-Loop. But we do know “when to stop” . We STOP when the cell

we are painting is already blue

We should use a: Do-Until-LoopCS 105 – Spring 2009 8

CS 105 – Spring 20099

Start

Is loopCondition

true?

End

Yes

Execute statements in loop body

No

Do-Until Loop Flowchart

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Syntax of a Do-Until Loops

Do-Until has the following syntax:Do Until <condition>

<…code to execute…>Loop

Pseudo-code:Do Until “the current cell is blue”

“paint the current cell blue” “move current cell one step to the

right”Loop

Paint until hitting a blue cell.

Do Until Cells(intRow, intCol).Interior.Color = vbBlue Cells(intRow, intCol).Interior.Color = vbBlue intCol = intCol + 1Loop

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‘NOTE: intRow and intCol hold the position of

‘the current cell

intRow = ActiveCell.RowintCol = ActiveCell.Column

Infinite Loop

When does the Do-Until-Loop finish? ONLY when the loop condition is TRUE What happens if the loop condition is never TRUE?

NOTE: The loop condition has to eventually be TRUE otherwise the loop will NEVER stop, becoming an infinite loop.

Use Ctrl-Break or Esc to terminate an infinite loop

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Brush until hitting blue cells.

We want to paint lines of mintBrushSize size until they we come across blue cells

How do we do this? We know how to draw one line, using a Do-Until-Loop We know how to do this mintBrushSize times, using a For-

Loop

We should use a: Do-Until-Loop nested inside a For-Loop

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Paint until hitting a blue cell.

For intOffset = 0 to mintBrushSize -1 intCol = ActiveCell.ColumnDo Until Cells(intRow +intOffset, intCol).Interior.Color =

vbBlue Cells(intRow+intOffset, intCol).Interior.Color = vbBlue intCol = intCol + 1Loop

Next intOffset

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‘NOTE: intRow and intCol hold the position of

‘the current cell

intRow = ActiveCell.Row

Finally, make a masterpiece !

We want to paint with a random color

VBA has 56 color index, ranging from1 to 56.

REMEMBER: To paint a particular cell with a color index we wrote:

….Interior.ColorIndex=[color_index]

How do we get a random color_index between 1 and 56? CS 105 – Spring 2009 15

Generate a random number

VBA provides a built-in function called Rnd() that gives a random floating-point number in [0,1).

How can we convert the random number provided by Rnd() into an integer between 1 and 56?

Answer : Int( Rnd() * 56 ) + 1 CS 105 – Spring 2009 16

0 1

Rnd()

Scaling up

Color Index

1 2 …. 55 56

0 56

Generate a random number (cont)

What if we want a random number between 2 and 10?

Answer : Int( Rnd() * (10-2+1) ) + 2

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0 1

Rnd()

Scaling up

Color Index

2 3 …. 10 11

0 9

Finally, make a masterpiece !

Private Sub cmdPaintRandom_Click()Dim intRow As IntegerDim intCol As IntegerintRow = ActiveCell.RowintCol = ActiveCell.Column 'TODO : call Randomize sub procedure

Randomize'Two variables to hold a random color index and random length

Dim intRandomLength As IntegerDim intRandomColor As IntegerDim intOffset As Integer'TODO : get a random integer between 1 and 56 and assign to intRandomColor

intRandomColor = Int(Rnd() * 56) + 1'TODO : get a random integer between 1 and 10 and assign to intRandomLength

intRandomLength = Int(Rnd() * (10-2+1)) + 2

'This is the incrementing variable for the For-loop'for loop to paint "mintBrushSize" cells at a time'TODO : use intRandomLength here

For intOffset = 0 To intRandomLength – 1'TODO : use intRandomColor hereCells(intRow + intOffset, intCol).Interior.ColorIndex =

intRandomColorNext intOffset

End Sub procedure to make it more random

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What you should know?

How to write a Nested-For-Loop? How to write a Do-Until-Loop

How to nest it inside a For-Loop How to generate a random integer

number?

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Exercises

Add more “Paint until Hit” buttons, each does a different direction : up, down, left, right

Do the same for “Paint Randomly”

Do the above, but this time, paint in 4 diagonal directions : North-East, South-East, South-West, North-West.

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Exercises

21

Do-Loop-While Do-Loop-Until Do-Until-LoopSub Test1 (intA As Integer) Do intA = intA + 1 Loop While intA < 10End Sub

Sub Test2 (intA As Integer)

Do intA = intA + 1 Loop Until intA < 10End Sub

Sub Test3 (intA As Integer)

Do Until intA >= 10 intA = intA + 1 LoopEnd Sub

Exercise

# Times

value of intA?

Exercise#

Timesvalue of

intA?Exercise

# Times

value of intA?

Test1(1) Test2(10) Test3(100)

Test2(1) Test3(10) Test1(0)

Test3(1) Test1(100)

Test1(-10)

Test1(10)

Test2(100)

Test2(9)