Previous Top Next

Regular variables

Regular variables are variables that hold a single value (unlike arrays or structures which hold multiple values).

Variables can be either global or sub local.
Local variables value can be used only while their parent sub is executing.
Global variables’ values can be used everywhere.
Global variables are variables that were declared (or used) in Sub Globals; all other variables are local.

As of v6.90 it is possible to declare the type of regular variables. The two main types are String and Number. By default all variables are Strings. Number type corresponds to .Net Double type which stores floating point values.
Other types available are Integer which holds whole numbers and Boolean which holds the values True and False.

Basic4ppc tries to convert numbers, strings and booleans values when required.
However it is highly recommended to declare numeric values as Numbers as mathematical calculations done with these variable are much faster (in the compiled code) compared to such calculations with String variables.

For example, the following code will work properly:
Dim s As String
Dim n As number
n = "42"
s = n & "1"
n = s 'n = 421

It is possible to use regular variables without any declaration. These variables will be of type String (which can hold all values).
An optional check is done for undeclared variables to make sure that each variable is assigned a value before its value is read and that each variable is eventually used.
This check can be disabled by unchecking Tools - Check for unassigned / unused variables.
See Modules for more information about global variables access modifiers.

(An error message will show if using the check unassigned variables.)
Sub Globals
End Sub

Sub App_Start
End Sub

Sub CalcVars
            Msgbox ("a = "  &  a)
            Msgbox ("b = "  & b)
End Sub

Result: First msgbox will show a = 20
            Second msgbox will show b =
b is empty because it's local and wasn't assigned any value yet in this sub.

To pass data between subs you could use global variables, or better, you can pass the data as parameters.

Sub Globals
End Sub

Sub App_Start
            CalcVars (c)
End Sub

Sub CalcVars (b)
            Msgbox ("a = "  &  a)
            Msgbox ("b = "  & b)
End Sub
Result: The second msgbox will show b = 10

Note: When using parameters the variable is not passed, but its value is copied.
          In the above example, I used a variable named c instead of b.
Remember that if you change a local variable’s value in one place (even if it had received its data from a parameter), then the change will not affect any other local or global variable outside the current sub. That unless the parameter is declared with ByRef.

Array Variables

Basic4ppc supports arrays of up to three dimensions.
Array variables are always global and must be declared before used.
Arrays can store items of a certain data type.
This is useful for working with external libraries which sometimes expect an array of a certain type.
Declare global variables with the Dim keyword.
See Array for a convenient method of initializing arrays.
The same array can be declared again with a different size any number of times during the program.
However, it must be first declared in Sub Globals (even with 0 items).
An array index starts from 0 and its last index is array dimensions - 1.
Sub Globals
            Dim Books (20)
            Dim Buffer (100) As Byte
End Sub

Result: Declares an array of 20 items starting from Books(0) and up to Books(19) and an array of bytes starting from Buffer(0) and up to Buffer(99)
When you need to reference an entire array (not one item in the array) write the array's name followed by ().
i = ArrayLen (buffer() )
BinaryFile.WriteBytes (buffer())

Arrays can be declared with 0 items like:
            Dim Buffer(0) As Byte
Buffer is an empty array that can be used later with an external library which returns an array.
Buffer() = Serial.InputArray

Structure Variables

Structures are variables with customized fields.
Using structures the code can be clearer and better organized.
Structures  must be declared in Sub Globals.
See the Dim keyword for information on declaring structures.
See Array for a convenient method of initializing structures.
Using regular structures is similar to using a control's properties.
Write the name of the variable followed by a period '.' and a list of the available fields will pop.
Sub Globals
            Dim Type(Name, ID, Age) person
End Sub

Sub App_Start
            person.Name = "John"
            person.ID = 1234567
            person.Age = 30
End Sub

You could also use arrays of structures (up to two dimensions):
Sub Globals
            Dim Type(Name, ID, Age) persons (100)
End Sub

Sub App_Start
            persons(0).Name = "John"
            persons(0).ID = 1234567
            persons(0).Age = 30
End Sub

- On the device only, you need to press on Subs - REFRESH in order that any declaration change will appear in the pop up list.
- You can reference the whole structure using the structure name followed by ().
Example: person() = SomeSub
- Structures are converted to arrays during the compilation.
In the first example, person will be an array of one dimension, person.Name = "John" will be converted to person (0) = "John" and so on.
You can also use the array syntax to work with structures.