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CS105 Lab 9 – Do-While-Loops

CS105 Lab 9 – Do-While-Loops. Announcements MP2 released today! See website for several important announcements/deadlines. Objectives. Develop a more sophisticated paint program Nested-For-Loop Do-Until-Loop Generate a random number. What we will do. Last week, we: Painted

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CS105 Lab 9 – Do-While-Loops

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  1. CS 105 – Fall 2009 CS105 Lab 9 – Do-While-Loops • Announcements • MP2 released today! • See website for several important announcements/deadlines

  2. CS 105 – Fall 2009 Objectives • Develop a more sophisticated paint program • Nested-For-Loop • Do-Until-Loop • Generate a random number

  3. CS 105 – Fall 2009 What we will do • 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

  4. CS 105 – Fall 2009 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? For intOffset = 0 To mintBrushSize – 1 Cells(intRow + intOffset, intCol).Interior.Color = vbBlue Next intOffset “+intOffset” ? “+intOffset” ? For intOffset = 0 To mintBrushSize – 1 Cells(intRow, intCol + intOffset).Interior.Color = vbBlue Next intOffset

  5. CS 105 – Fall 2009 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 Nested-If • 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

  6. CS 105 – Fall 2009 Paint a square For intRowOffset = 0 To 4 For intColOffset = 0 To 4 Cells(intRow + intRowOffset, intCol + _ intColOffset).Interior.Color = vbBlue Next intColOffset Next intRowOffset • Dim intRowOffset As Integer • Dim intColOffset As Integer Tip: to observe the nested For-Loop step by step you can call the “Delay” sub here

  7. CS 105 – Fall 2009 Paint a square, with the ActiveCell in the center • The previous code painted a square to • the right and bottom of the ActiveCell. How can we draw it aroundtheActiveCell? For intRowOffset = -2 To 2 For intColOffset = -2 To 2 Cells(intRow + intRowOffset, intCol + _ intColOffset).Interior.Color = vbBlue Next intColOffset Next intRowOffset

  8. CS 105 – Fall 2009 Paint until it hits a blue cell. • We want to paint a line from the the ActiveCell, until it hits another cell 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-Loop

  9. CS 105 – Fall 2009 Do-Until Loop Flowchart Start Is loop Condition true? Execute statements in loop body No Yes End

  10. CS 105 – Fall 2009 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

  11. CS 105 – Fall 2009 Paint until hitting a blue cell. Do Until Cells(intRow,intCol+intColOffset).Interior.Color = vbBlue Cells(intRow, intCol+intColOffset).Interior.Color = vbBlue intColOffset = intColOffset + 1 Loop ‘NOTE: intRow and intCol hold the position of ‘the current cell intRow = ActiveCell.Row intCol = ActiveCell.Column intColOffset = 0

  12. CS 105 – Fall 2009 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

  13. CS 105 – Fall 2009 Brush until hitting blue cells. • We want to paint lines of mintBrushSize size untilthey 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

  14. CS 105 – Fall 2009 Paint until hitting a blue cell. ‘NOTE: intRow and intCol hold the position of ‘the current cell intRow = ActiveCell.Row For intOffset = 0 to mintBrushSize -1 intCol = ActiveCell.Column Do Until Cells(intRow +intOffset, intCol).Interior.Color = vbBlue Cells(intRow+intOffset, intCol).Interior.Color = vbBlue intCol = intCol + 1 Loop Next intOffset

  15. CS 105 – Fall 2009 Finally, make a masterpiece ! • We want to paint with a random color • VBA has 56 color index, ranging from 1 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?

  16. CS 105 – Fall 2009 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 0 1 Rnd() Scaling up 0 56 Color Index 1 2 …. 55 56

  17. CS 105 – Fall 2009 Generate a random number (cont) • What if we want a random number between 2 and 10? • Answer : Int( Rnd() * (10-2+1) ) + 2 0 1 Rnd() Scaling up 0 9 Color Index 2 3 …. 10 11

  18. CS 105 – Fall 2009 Finally, make a masterpiece ! Private Sub cmdPaintRandom_Click() Dim intRow As Integer Dim intCol As Integer intRow = ActiveCell.Row intCol = ActiveCell.Column 'TODO : call Randomize sub procedure Randomize 'Two variables to hold a random color index and random length Dim intRandomLength As Integer Dim intRandomColor As Integer Dim 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 here Cells(intRow + intOffset, intCol).Interior.ColorIndex = intRandomColor Next intOffset End Sub procedure to make it more random

  19. 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?

  20. 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.

  21. Exercises

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