Fundamentals of BASIC

Variables

Naming

The following list shows some variable names that are allowed by AppStudio:

text
LLAMAS
Jupiter
W1Spec
SouthPark

And some that are not allowed:

1table          'starts with a number 
X&Ycords        'uses special character & 
first counter   'has a space 
%correct        'does not start with a letter
print           'Keyword

Variables

• All variables are of type Variant.
• No explicit types
• Variable get their types from the value that is assigned.

Numeric

• Floating point: 5e-324 (negative) to 1.7976931348623157e+308 (positive)
• Integers: reliable to 15 digits.
• Hex: 0x500 = 1280
• Octal: O500 = 320

Booleans

• True or False.

Colors

• From “#000000” to “#FFFFFF” (black to white)
• color = (red*65536) + (green * 256) + blue

Strings

• Maximum length depends on memory, up to 2 billion characters

Arrays

• Dim A(9) declares an array with 10 elements
• Dim B(8,8) creates a two dimensional array
• Elements can be referred to as A(3), B(2,3), etc.
• Dim statement has to be in each Code Module
• The following notation is also OK: a[3], B[2][3}
• Array elements do not exist until they are assigned.

Collections

• Like an Array, but uses string values to index

Dim item1, myCollection(10)
item1="Knuth"

'Create our collection
myCollection[item1] = "firstKey"
Print myCollection[item1]  'displays "firstkey"

Objects

• An object is a collection of named values, called properties

Customer={Name: Lovelace, Age: 195, kids:{Byron: 1, Annabella: 2, Ralph: 3}}
Print Customer.name  'displays "LoveLace"

Classes

'Define a class like this
Function Person(name, gender)
   'Add object properties like this
   this.name = name
   this.gender = gender
End Function

'Add methods like this.  All Person objects will be able to invoke this
Function speakName()
  Print "Howdy, my name is " & this.name
End Function

Person.prototype.speak = Eval("speakName")

'Instantiate new objects with 'new'
bob = new Person("Bob", "M")

'Invoke methods like this
bob.speak() 'Prints "Howdy, my name is Bob"

Control structures

If...Then

If a=b Then c=1

If a=b Then
  c=1
End If

If a=b Then
  C=1
Else
  C=2
End If

Loops

For i=1 to 10
  Print i
Next

i=0
Do While i<10
  Print i
  i=i+1
Loop

i=0
Do
  Print i
  i=i+1
Loop Until i=10

Rem While...Wend Example
'While...Wend repeats a group of statements

Dim Counter
Counter = 1
While Counter < 5
  Print "Counter = " & Counter
  Counter = Counter + 1
Wend

With

Rem With sample
'With statement allows accessing properties on a specified object

Dim theURL, theTitle
With document
  theURL = .URL
  .title = "New Title"
  theTitle = .title
  Print .URL
  Print .title
End With

Select Case

Rem Select Case Example
'Select Case performs conditional execution
CheckHat("Blue")
CheckHat("Orange")
Sub CheckHat(Hat)
  Select Case Hat
  Case "Blue"
    Print "Kyle's hat"
  Case "Green"
    Print "Stan's hat"
  Case "Cyan"
    Print "Eric's hat"
  Case "Orange", "Hood"
    Print "Kenny's hat"
  Case "White"
    Print "Chef's hat"
  Case "Striped"
    Print "Mr. Hat"
  Case "Christmas", "Santa"
    Print "Mr. Hankey's hat"
  Case Else
    Print "Unknown Hat"
  End Select
End Sub

Error trapping

Rem Try Example
'Try catches run time errors
Try
   Dim CurrLiab, CurrAssets 
   CurAssets=InputBox("Enter assets")
   If Not IsNumeric(CurAssets) Then Throw 1
   If CurAssets < 0 Then Throw "lessthan"
   CurLiab=InputBox("Enter liabilities")
   If CurLiab=0 Then Throw "Divide by Zero"
   If CurLiab < 0 Then
      Throw "Liabilities must be > 0"
   End If
   If Not IsNumeric(CurLiab) Then Throw 1
   Print CurAssets, CurLiab
   Print "Ratio:" & CurAssets/CurLiab
Catch err
   If err=1 Then err="Enter a number"
   If err="lessthan" Then
      err="Value must be >= 0"
   End if
   Print err
Finally 'this is optional
   Print "Done"
End Try

Functions and Subroutines

Sub mySubroutine(a,b)
  Print a + b
End Sub

Function myFunction(a,b)
  myFunction = a + b
End Function