Learn to Program with Small Basic

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Two Kinds of Data Programs use all different types of data: applications that do calculations use numbers, but others might use text. Small Basic uses very simple data types. It has built-in support for just two data types: numbers and strings. Numbers can be integers, like –2 and 2365, or decimal numbers, like 0.25 and –123.78. As you know, strings are characters strung together between double quotation marks, like "The Declaration of Independence" or "She sells seashells by the seashore." You don’t need to tell Small Basic what type of data you’re going to store in a variable. This is a beginner-friendly way of programming. Global Variables Variables in Small Basic are global in scope. This means you can define a variable and access a variable from anywhere in your program. This feature is helpful because it lets you define variables just when you need them (instead of having to put all your variables at the top of your program). But you have to be careful! Because Small Basic reads your programs in order, it’s possible to create logical errors. Try the program in Listing 4-3. 1 ' LogicError.sb 2 y = x / 10 3 x = 20 4 TextWindow.WriteLine("y = " + y) Listing 4-3: Logic error with global variables If you’re reading this code closely, you’ve already noticed that, in line 2, we’re using the variable x before we’ve assigned it any particular value. When we run this code, we get the following output: y = 0 Does that answer surprise you? Here’s what’s happening. When the Small Basic compiler reads this code, it first makes a list of all the variables you defined in the program. The initial values for these variables are left empty, like empty boxes. As long as the expressions in the program use variable names from that list, the compiler’s happy and the program will run. When the program runs the expression x / 10 in line 2, it interprets x as a number because division only makes sense for numbers. That’s why it fills the empty box for x with 0. It then assigns the result of the division (which is 0) to y. The variable x is changed to 20 in line 3, but it’s too late! You get the wrong output. Using Variables 53
Note Most other programming languages would report a syntax error because the expression x / 10 in line 2 uses a variable x that hasn’t been defined yet in the program. Small Basic lets you define variables anywhere in your program; just don’t expect to get away with it in other languages. Be careful when you order your statements because Small Basic runs top to bottom. Make sure you define your variables before you use them for the first time. TRY IT OUT 4-5 What’s the output of this program? Explain what you see. TextWindow.WriteLine("Before: x = " + x + " and y = " + y) x = 10 y = 10 TextWindow.WriteLine("After: x = " + x + " and y = " + y) Programming Challenges If you get stuck, check out http://nostarch.com/smallbasic/ for the solutions and for more resources and review questions for teachers and students. 1. Do you like knock-knock jokes? Try the following program to see how to tell them in Small Basic! Which program lines do you need to change to tell a different joke? Make the change and run the program again to see what happens: ' KnockKnock.sb ' Small Basic can tell knock-knock jokes! name = "Orange" reply = "you going to answer the door?" TextWindow.WriteLine("Knock Knock") TextWindow.WriteLine("Who's there?") TextWindow.WriteLine(name) TextWindow.WriteLine(name + " who?") TextWindow.WriteLine(name + " " + reply) TextWindow.WriteLine("") 2. Translate this pseudocode into a Small Basic program: a. Set quantity to 10. b. Set item price to 15 dollars. c. Compute total price by multiplying quantity by item price. d. Display total price. 54 Chapter 4
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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
Page 28 and 29: BASIC language that would help kids
Page 30 and 31: Toolbar Help Area Editor Surface Fi
Page 32 and 33: Then click the New button to open a
Page 34 and 35: Helping Hands: IntelliSense and Syn
Page 36: 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 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 88 and 89: The For loop runs Turtle.Move(60) a
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
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Your mom’s instructions assume th
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But wait, your mom just realized th
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This code asks the user to enter a
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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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