BlitzMax/Language/Variables

From Wikibooks, open books for an open world
Jump to: navigation, search

Variables are used to store values that change during the execution of your program.

Variables should be declared in your program before use. Declaring a variable means defining a name and type for the variable and, optionally, an initial value.

The general syntax for declaring a variable is:

Declaration Identifier : Type = Expression

Multiple variables may be declared in one statement using the comma separator.

If the type of a variable is omitted, the variable defaults to being of type Int. If the initial value expression is omitted, the variable is assigned an initial value of Null.

There are 3 kinds of variable, each of which differs by how and where the variable is stored:

Local Variables[edit]

Local variables are used to store temporary values that will eventually be discarded. Local variables are associated with the block of code they are declared in, and are only visible to code within that block. A block of code is represented by one of the following:

  • The body of a function or loop
  • The body of an if/then/else statement
  • The body of a case or default statement

To declare a local variable, use a Local declaration:

Local int_var
Local string_var:String="Str",float_var:Float=10.5

Comment: You should prefer the use of local variables, as they are the fastest to use.

Global Variables[edit]

Global variables are variables that exist for the entire lifetime of a program.

To declare a global variable, use a Global declaration:

Global int_var
Global string_var:String="Str",float_var:Float=10.5

Field Variables[edit]

Field variables are declared within user-defined types using a Field declaration:

Field int_var
Field string_var:String="Str",float_var:Float=10.5

See the user-defined types section for more on field variables.

Assigning variables[edit]

Once declared, a variable's value may be changed using an assignment statement:

Variable = Expression

You can also perform 'modifying' assignments, which are shorthand for Variable = Variable Operator Expression. The syntax for modifying assignments is:

Syntax Operator
 :+ Addition
 :- Subtraction
 :* Multiplication
 :/ Division
 :Mod Remainder
 :& Bitwise and
 :| Bitwise or
 :~ Bitwise exclusive or
 :Shl Bitwise shift left
 :Shr Bitwise shift right
 :Sar Arithmetic shift right

For example, the code my_var:+1 can be used in place of my_var=my_var+1.