Learn to Program with Small Basic

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The For loop runs Turtle.Move(60) and Turtle.TurnRight() four times. You use a For loop when you know how many times you want to repeat some code (for more on For loops, see Chapter 13). In this example, your program starts the loop, runs the two lines of code, and then goes back to the start of the loop to run it again. It runs four times and then exits the loop. Try it out! In this short program, you’re using three new Small Basic keywords: For, To, and EndFor. NOTE The keywords (For, To, and EndFor) don’t have to be capitalized the way you see them in Listing 5-7, and the statements in the For loop don’t have to be indented, but those are the default formats. The Editor indents the statements inside the For loop as you type to make your code easier to read. Figure 5-10 shows what’s going on. This is the loop’s counter. You can call it anything you want. In this chapter, this will always be 1. For I = 1 To 4 Turtle.Move(60) Turtle.TurnRight() EndFor This is how many times you want to repeat the code. Put the statement(s) you want to repeat between the For and EndFor keywords. Figure 5-10: The parts of the For loop To repeat lines of code, you simply put the statement(s) you want to repeat between the For and EndFor keywords. If you want to repeat these statements four times, write this: For I = 1 To 4 The variable I is the counter. It keeps track of how many times the loop has been run and how many times it has left to go. Each time your program runs the loop, it adds one to the counter. Remember the For loop the next time you get in trouble at school! If your teacher catches you chewing gum and asks you to write I won’t chew gum in class again 100 times, Small Basic is there to rescue you! Write this instead: For I = 1 To 100 TextWindow.WriteLine("I won't chew gum in class again.") EndFor Try it out. No, not chewing gum in class; try out the program! Drawing Shapes with Turtle Graphics 63
NOTE Programmers usually use one-letter variables to name the loop’s counter (such as I, J, or K), but any other name works too. It doesn’t matter if you use upper- or lowercase letters—Small Basic would treat I and i as the same variable. TRY IT OUT 5-2 Predict the output of the following program. Then run the program to check your answer. GraphicsWindow.PenColor = "Red" GraphicsWindow.PenWidth = 3 For I = 1 To 4 Turtle.Move(30) Turtle.Turn(-60) Turtle.Move(30) Turtle.Turn(120) Turtle.Move(30) Turtle.Turn(-60) Turtle.Move(30) Turtle.TurnRight() EndFor Drawing Regular Polygons You can easily change the square-drawing program (Listing 5-7) to draw other polygons. (Don’t be so square!) A polygon is just a simple closed figure. For some examples, look at the three polygons in Figure 5-11. 90° 60° 72° Figure 5-11: The exterior angles of three polygons You use a general pattern to draw these shapes. To create the square in Figure 5-11, you draw four sides with a 90-degree turn angle after each side (that is, 360 degrees divided by 4). For the pentagon (the middle polygon), you draw five sides with a 72-degree turn angle after each side (360 divided 64 Chapter 5
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Learn to Program with Small Basic A
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Learn to Program with Small Basic A
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Brief Contents Foreword by Vijaye R
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Exploring Other Features. .........
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7 Empowering Programs with math 83
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12 building Graphical User Interfac
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Storing Records. ..................
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Foreword Computer programming is ma
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Acknowledgments This book represent
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Introduction Have you ever wondered
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• In Chapter 11: Event-Driven Pro
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1 Introducing Small Basic Bill Gate
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BASIC language that would help kids
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Toolbar Help Area Editor Surface Fi
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Then click the New button to open a
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Helping Hands: IntelliSense and Syn
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Programming Challenges If you get s
Page 39 and 40: The Parts of a Program Let’s expl
Page 41 and 42: The method’s name and a brief des
Page 43 and 44: 5 + 7 12 Here’s the output of thi
Page 45 and 46: For example, to make the TextWindow
Page 47 and 48: TRY IT OUT 2-3 Now you have a chanc
Page 49 and 50: Programming Errors Just because a p
Page 51 and 52: 26 Chapter 2 4. Write a program tha
Page 53 and 54: In the system you use at school, po
Page 55 and 56: Drawing Shapes You can draw lots of
Page 57 and 58: Figure 3-6 shows what the output lo
Page 59 and 60: 22 GraphicsWindow.BrushColor = "Lig
Page 61 and 62: DrawText() takes three arguments. T
Page 63 and 64: GraphicsWindow provides two methods
Page 65 and 66: 6. Write a program that draws this
Page 68 and 69: 4 Using Variables Have you ever wan
Page 70 and 71: Try changing the value in karenBear
Page 72 and 73: These two ways of updating the scor
Page 74 and 75: Figure 4-2: How a variable is added
Page 76 and 77: TRY IT OUT 4-3 Write a program that
Page 78 and 79: Two Kinds of Data Programs use all
Page 80 and 81: 5 Drawing Shapes with Turtle Graphi
Page 82 and 83: Absolute Motion With absolute motio
Page 84 and 85: North 0 (360) 315 (-45) 45 (-315) W
Page 86 and 87: GraphicsWindow.PenColor = "Red" Gra
Page 90 and 91: y 5). For the hexagon (the polygon
Page 92 and 93: Creating Polygon Art Using Nested L
Page 94 and 95: Endless Graphics In Listing 5-10 yo
Page 96: Write a program to have the turtle
Page 99 and 100: Talking to the Computer Until now,
Page 101 and 102: Figure 6-2: The text window waiting
Page 103 and 104: 4 C = (5 / 9) * (F - 32) 5 C = Math
Page 105 and 106: 9 noun = TextWindow.Read() 10 11 Te
Page 108 and 109: 7 Empowering Programs with Math If
Page 110 and 111: Here’s a sample run of our progra
Page 112 and 113: Round() -4 -3.5 -3 0 3 3.5 4 Round(
Page 114 and 115: This code snippet shows you some ex
Page 116 and 117: Let’s walk through this program l
Page 118 and 119: Trigonometric Methods Trigonometric
Page 120: Programming Challenges If you get s
Page 123 and 124: Small Basic uses a few different wa
Page 125 and 126: You can test all sorts of condition
Page 127 and 128: Small Basic first finds the value o
Page 129 and 130: Your mom’s instructions assume th
Page 131 and 132: But wait, your mom just realized th
Page 133 and 134: This code asks the user to enter a
Page 136 and 137: 9 Using Decisions to Make Games Som
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Condition 1 True Statement set 1 If
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This change to the program means th
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Door 1 Door 2 Door 3 Figure 9-6: Pe
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Listing 9-4 shows an example of usi
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Think of the Shapes object as a “
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Background image (Grid.png) Star.pn
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In Figure 9-8, you see that the gri
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This code asks the player to enter
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10 Solving Problems with Subroutine
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Gulliver later learned that 1 glum-
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TRY IT OUT 10-1 When Gulliver asked
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variables that belong to the main p
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4 TextWindow.WriteLine("Your turn.
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1 step away). If the arrow hits the
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Then you set the graphics window’
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24 Shapes.SetText(msgText, "") 25 T
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Step 8: Shoot Arrows with ShootArro
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Lines 3-7 animate the dragon’s fi
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11 Event-Driven Programming So far,
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GraphicsWindow Events Let’s start
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4 5 Sub OnKeyDown 6 GraphicsWindow.
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13 Else 14 GraphicsWindow.DrawText(
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Useful Tips Before moving on, we’
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21 GraphicsWindow.BrushColor = "Red
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4 XG = Math.GetRandomNumber(8) - 1
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Programming Challenges If you get s
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Today, most programs use a graphica
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located at (100, 100). By default,
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9 GraphicsWindow.MouseMove = OnMous
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Let’s look at the computations. Y
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You start by loading the two backgr
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(line 8). If the total resistance i
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TRY IT OUT 12-4 Write a program to
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13 Repeating For Loops Have you eve
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Each For loop starts with the keywo
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The program uses a variable named s
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TRY IT OUT 13-5 What does the follo
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Nested Loops The statements in the
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Figure 13-7: The output of Stamp.sb
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2. Although the pizza in the previo
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In this chapter, you’ll learn how
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Note Although it’s not required b
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asks the user for the correct answe
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to become a value other than 0 (thi
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Step 4: Announce the Winner The las
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15 Grouping Data in One-Dimensional
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One way to think of an array is as
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The string initializer lets you fil
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TextWindow.WriteLine("Enter 5 numbe
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how much money was rescued from eac
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To create this program, we’ll use
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The apples fall from the trees. Usi
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The subroutine uses a For loop to c
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9 If ((xdiff < 20) And (ydiff < 20)
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4. Open the file USMapQuiz_Incomple
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Associative Arrays In the previous
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The expression If("ernie" = "Ernie"
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Here’s the output from a sample r
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The ContainsIndex() method takes tw
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Figure 16-1 shows the user interfac
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1 Sub OnButtonClicked 2 GraphicsWin
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17 Expanding to Higher-Dimension Ar
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1 ' Random2DArray.sb 2 For r = 1 To
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Animated Squares Let’s write a pr
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12 TextWindow.Write("Enter student
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(line 8). Line 9 displays Scott's M
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You start by initializing the sum v
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4 For col = 1 To 4 ' For each colum
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note If you run into any problems,
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First, you set all the elements of
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11 If ((rowP < 1) Or (rowP > 10) Or
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Open the file Okla.sb from this cha
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(both uppercase and lowercase), dig
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Taking Strings Apart: Substrings Ju
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two arguments: the source string th
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Here’s an output example: Who's y
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More on Code Points The Unicode cod
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Line 7 gets the Nth character of th
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Igpay Atinlay Let’s teach the com
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17 TextWindow.WriteLine("Good Job!"
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9 pos = Math.GetRandomNumber(len) '
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When you continue with the second a
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TRY IT OUT 18-10 Use the techniques
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19 Receiving File Input and Output
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and their meanings. File extensions
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program’s folder (right-click the
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in the file would run together in o
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Let’s experiment with the first p
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line number. As with the WriteLine(
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WARNING If the destination path poi
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6 For N = 1 To count ' Displays the
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wizard asks the user to perform. Th
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Figure 19-8 shows a sample run of t
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Where to Go from Here So you’ve m
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Index Numbers and Symbols 3DArrayDe
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squares, 31-32 star, 65-66 triangle
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integrated development environment
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parts of, 14-16 publishing, 5-6 run
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NewGame() subroutine, 255-256 OnBut
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ages 10 and up “Welcome to the ma
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Learn to Program with Small Basic

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