Variables hold information (data) about a video game and the game objects in it. Things like a character's name or hit points. Anytime you need you need to reserve computer memory to store a single number or single piece of text, you will store them in a variable.

' Example in FreeBASIC
dim pname as string
pname = "Soliztan Margot"
print pname
sleep
end

Declaration of Variables

In some BASIC dialects, Dim is used to declare (or create) a variable. This associates the identifier with a memory location. In layman's terms, it is simply creating a variable to hold stuff.

Implicit Declaration

Many programming languages allow you to ''implicitly'' declare variables, that is, to have them created during the first time they are used. For example, when you use the assignment operator without first declaring a variable, it is created when this code is run :

10 REM CBM BASIC ONLY HAS IMPLICIT VARIABLE
20 REM DECLARATION. 
30 REM
40 REM EXPLICIT DECLARATION IS USED ONLY
50 REM FOR ARRAYS (SUBSCRIPTED VARIABLES)
60 REM 
70 LC$ = "THE GRIM HALL"
80 PRINT LC$
90 END

location$ = "The Grim Hall" ; the variable is created here.

Print location$
Sync
WaitKey

Explicit Declaration

Some programming languages force you to ''explicitly'' declare variables, that is, to create them before you use them. This is done with DIM.

' FreeBASIC Example
dim location as string
location = "The Grim Hall"

Explicit declaration of variables is usually done at the beginning of your game code.

Explicit and Implicit Declaration

Some programming languages expect you to use implicit declaration by default (especially modern BASICs) and allow you to explicitly declare variables as you so choose. Most of these languages, such as FreeBASIC and Brutus2D allow you to force the explicit declaration of variables if you so choose. In that case, OPTION EXPLICIT can be used.

If OPTION EXPLICIT is used, then any variable not explicitly declared will result in an error. This saves bugs from misspellings because if you misspell the variable's name, OPTION EXPLICIT will cause an error because the misspelling has not been explicitly declared.

Data Type

(Full article : data type)
The "data" stored in variables usually has to be of a specific type. The most common data types are strings and numbers.

String variables are used for holding messages and other things dealing with ''text''.

Numeric variables are used for math-related operations such as hit points.

Local and global variables

Some programming languages allow specification of local and global variables.

Local variables are available for read and write only within given procedure ( function, sub ).

PSub Procedure1()
  LOCAL myText$ = "From procedure 1"

  myNumber = 1

  Procedure2()
ENDPSub

PSub Procedure2()
    Print myText$
  ; -- From here the myText$ variable is not "visible"
ENDPSub

Procedure1()
Sync
WaitKey

SUB Procedure1()
  LOCAL myNumber AS INTEGER

  myNumber = 1

  Procedure2()
END SUB

SUB Procedure2()
  ' -- From here the myNumber variable is not "visible"
END SUB

Global variables are available for read and write from any part of the program.

GLOBAL myGlobalVar AS INTEGER

SUB Procedure1()

  ' -- I can assign to global variable from any where
  myGlobalVar = 1

END SUB

SUB Procedure2()

  ' -- I can assign to global variable from any where
  myGlobalVar = 2

END SUB

GLOBAL myGlobalVar

PSub Procedure1()

  ; -- I can assign to global variable from any where
  myGlobalVar = 1

ENDPSub

PSub Procedure2()
    Print myGlobalVar
  ; -- I can assign to global variable from any where
  myGlobalVar = 2
  Print myGlobalVar

ENDPSub

Procedure1()
Procedure2()
Sync
WaitKey

Swapping Variable Values

If you want to swap (or switch) the value of two variables, you will need one more variable as a "buffer". First, here's the wrong way to do it :

var1 = 1
var2 = 2
var1 = var2
var2 = var1

This will result in var1 and var2 having the same value (2). The value in var1 was overwritten in line 3. So, to make this work properly, you must store the value of var1 in a kind of variable "buffer".

var1 = 1
var2 = 2
varb = var1
var1 = var2
var2 = varb

This will accomplish the task of switching two variable's values.

Many programming languages make swapping of variables more easy, using SWAP command:

var1 = 1
var2 = 2

SWAP var1, var2

Now var1 equals to 2 and var2 to 1

Uses for Variables

Accelerator Variable

An accelerator variable is a variable that represents the speed of acceleration of something. It works by adding the value of the accelerator variable to the one being accelerated each game loop.

For example gravity is a very common accelerator variable. It is added to the vertical speed of the object :

vSpeed = vSpeed + gravity

When this is done, vSpeed is accelerated at a constant rate - the rate of gravity.

Accelerator variables do not always have to be related to physics. In a forest fire simulation, an accelerator could represent the acceleration of the spread of the fire.

' acres = acres burned per game loop
acres = acres + spreadOfFire

Some programming languages allow shorter syntax for this type of addition, using += operator. So the examples above could be written as:

vSpeed += gravity

acres += spreadOfFire

Accumulator Variable

An accumulator variable is any variable used to accumulate a total.

Accumulator variables are used like buckets. If you put a pint of water into a bucket and then put another pint of water in the bucket, you have ''accumulated'' two pints of water in your bucket.

Some applications for accumulator variables :

• The score of a game.
• The experience of a RPG character.
• Money or coins collected.

Others

• counter variable
• flag variable
• jump flag
• state variable

Related Pages

• LET - assign a value to or change the value of a variable.
• array - like a variable, but it can hold many values instead of one
• list of common variable names

Backlinks

These pages link back to this page. You may find them helpful.

Links

• Variables at the Basic4GL Wiki
• Variables at the Game Maker Wiki
• Variables at the PlayBasic Wiki
• Variables at the thinBasic Wiki

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