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Variable Declaration ( Dimensioning)Edit
In Gambas it is necessary to declare every variable. To dimension a variable, the code is:
Dim variablename as type
You can just skip the word Dim , so the following is also correct:
variablename as type
The variable name could be whatever you want. The type however has to be chosen. You have a choice of integer, string, variant and some others. This tells the computer what type of information the variable holds. Singles and integers hold numbers, while strings hold text.
'Dimensioning Dim i as Integer Dim x as Variant 'assignment i = 31 'This is ok i = "i do" 'Error: type mismatch(i is an integer;"i do" is a string) x = 341 'This is ok x = "books" 'This is all right
In Gambas you cannot dim an array as you were used in VB. The following is wrong:
xxxxx Dim x(1 to 10) as integer xxxxxx
Dimensioning can also be used to tell the computer that variables are public or private. When a variable is public, it may be used and changed in all sub-programs. To make a variable public you must dim it in the "declarations" area of the code. These declarations are placed on the very first lines in your code, above all sub programs and other code.
Examples: You need a command button on your form to get it going.
PUBLIC SUB Button1_Click() 'Declaration x AS integer y AS float z AS String 'assignment x = 2 y = 2.378 z = "That ist correct" 'the use of variables print x,y,z,x*y END
The following program will cause an error: x already declared
'xxxxxxxxxxxxxxxxxxxx PUBLIC SUB Button1_Click() DIM x AS integer DIM x AS float DIM x AS String x = 2 x = 2.378 y = "That ist not correct" print x,x,x END 'xxxxxxxxxxxxxxxxxxxxxx
In the following program you also cause some error warnings, as there is no difference between upcase and lowcase signs in Gambas.
PUBLIC SUB Button1_Click() DIM x AS integer DIM X AS float DIM x$ AS String x = 2 X = 2.378 x$ = "that ist correct " print x,X,x$ END
List of Gambas predefined datatypes for the declaration of variablesEdit
|Name||Description||Memory size||Default value|
||True or False||1 byte||False|
||0 ... 255||1 byte||0|
||-32768 ... +32767||2 bytes||0|
||-2147483648 ... +2147483647||4 bytes||0|
||Like the double datatype in C||8 bytes||0.0|
||Date and time, each stored in an integer .||8 bytes||Null|
||A reference to a variable length string.||4 bytes||Null|
||Any datatype.||12 bytes||Null|
||A anonymous reference to an object.||4 bytes||Null|
Once you have declared a variable , you can assign a value to it.
Variable = Expression
This will assign the value of an expression to one of the following elements :
- A local variable.
- A function parameter.
- A global (class) variable.
- An array slot.
- An object public variable.
- An object property.
iVal = 1972 Name = "Gambas" hObject.Property = iVal cCollection[sKey] = Name
Some versions of basic, allow structured variables to be created by using TYPE definitions as follows:
' This will not work in gambas TYPE rhubarbstructure foo AS STRING * 32 bar AS INTEGER END TYPE
PUBLIC rhubarb AS rhubarbstructure
Currently, gambas does not support the TYPE keyword. However, it is possible to use class definitions for the same effect.
Creating a classEdit
From the Integrated Development Environment file, create a class file rhubarbstructure.class as follows:
PUBLIC foo AS STRING PUBLIC bar AS INTEGER
It is now possible to define a variable utilizing that class, by creating an appropriate definition in the code module as follows:
DIM rhubarb AS rhubarbstructure