Fundamentals of BASIC

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Variables

Naming

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

text
LLAMAS
Jupiter
W1Spec
SouthPark
btnSubmit
txtCustomer

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
  • Variable names are case sensitive.
  • If you DIM a variable name, AppStudio will correct the case on entry.

Variables

  • All variables are of type Variant.
  • No explicit types
  • Variable get their types from the value that is assigned.
  • Variables Dimmed outside of an Function or Sub are global.
  • Variables Dimmed inside a Function or Sub are local.
  • Variables which are not declared are global.

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.
  • To create empty array, do this: a=[]
  • Use the Ubound() function to get the number of items in an array.

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
b=1
c=0
Try
  If c=0 Then throw "Division by zero!"
  a=b/c
Catch err
  Print err
Finally
  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

Importing VB code

  • Code using the above statements can usually be pasted in
  • Remember to remove the AS clauses
  • Simple controls (Buttons, TextBoxes, etc) have similar properties
  • Advanced controls and properties may be different

A few interesting statements