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Basic Compatibility

This section covers some of the differences between BlitzMax and 'classic' BASIC, and introduces features that help overcome some of classic BASIC's shortcomings.

Strict mode

Classic BASIC allows you to declare variables on the fly. For example, consider a program consisting of:

For k=1 To 10
    sum=sum+k
Next
Print sum

This program automatically creates 2 local variables: k and sum. However, this behaviour can often lead to unexpected bugs. For example, if you mistyped one of the sum variables, the program would not work as expected. No error would be given - a new variable would simply be created.

By default, BlitzMax NG implements what is known as Strict mode to override this behaviour.

Strict must appear at the top of your program before any actual program code and puts your program into strict mode. Strict mode forces you to declare all variables before use. For example, rewriting the above program in strict mode results in:

Strict
Local sum, k
For k = 1 To 10
    sum = sum + k
Next
Print sum

If you were to mistype one of the variable names in this program, you would receive an identifier not found error when compiling, allowing you to easily find and correct the problem.

In Strict mode, a variable whose type is not declared is assumed to be an Int.

SuperStrict mode

For even greater strictness, there is also SuperStrict mode. SuperStrict mode forces you to declare the type of each of your variables, as well as the return types of functions and methods. This can further assist in solving issues in your program by eliminating potential variable type confusion.

Rewriting the above program in SuperStrict mode results in:

SuperStrict
Local sum:Int, k:Int
For k = 1 To 10
    sum = sum + k
Next
Print sum

With all your variables strongly typed the compiler will be less forgiving and provide you with better errors if you attempt to mix incompatible variable types together.

Arrays

Blitzmax does not support the Dim statement for array creation. Instead, arrays in BlitzMax are real types - they can be passed to functions, returned from functions and placed in variables.

To create a classic BASIC style array in BlitzMax, use a global variable. For example:

Global my_array$[100]   ' create a 100 element string array

Also note that arrays in BlitzMax are not 1 bigger than their dimensioned size - the 100 element array above contains 100 elements, numbered 0 through 99 inclusive.

BlitzMax also does not support a Redim operation. Instead, you can use slices. For example:

Global my_array$[100]       ' create a 100 element string array
my_array=my_array[..200]    ' now a 200 element array!

Data, Read and Restore

Data, Read and Restore are supported but have been renamed to DefData, ReadData and RestoreData. Data labels must also be prefixed with a # character.

Type tag shortcuts

When declaring variables and function return types, BlitzMax allows you to use BASIC style type tags. These are as follows:

Type tagEquivalent type
%Int
#Float
!Double
$String

For example, a string variable can be declared in two ways:

Local a_string:String
Local another_string$

Mac users whose keyboards do not feature the # character should use Alt 3.

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