GAMBAS BOOK 3.19.5

Data types are required if you want to store data - as character-bound information - in a variable. Describe data types:

• what kind of data can be stored in a variable,
• the range of values that a certain data type covers,
• the permitted operations for the selected data type and
• the representation of the data in the memory, which determines how much memory is made available for a variable of a certain type.

There are native data types in Gambas. These include, for example, data types with the names (keyword), integer, byte, string or float. An overview of the native data types can be found in table 7.0.1 The syntax of a structure has been introduced in Gambas 3. These structures allow you to combine logically relevant IT units (both data types and classes or objects) into a new unit - a structure. However, this structure has no methods or events. Of particular importance in Gambas as an object-oriented language are the classes. Anything that is not a data type, structure, or executable code is a class. They are characterised by the fact that they are a logical encapsulation of properties, methods and events. An instance of a class is called an object.

Summary

• Gambas has native data types that carry their value information according to their type. The system checks whether the value assigned to a variable or constant collides with the declared data type.
• The structures are a bundling of different but related value information.
• In addition to the information (properties), classes also have methods to modify them and events to interactively act.

Thus, structures take a mediatingposition between the native data types and the abstract classes (concrete and abstract in the sense of their definition).

Table 7.0.1: Overview of the native data types in Gambas

The native data types have an associated array data type whose name corresponds to the name of the native data type and follows the square brackets: {code_b_0}

The description of arrays can be found in chapter 20.12.

You can use the following functions to determine the data type. The argument passed to the data type functions is a string or a data type in SizeOf () or an expression in TypeOf (). The function value is either True or False or a memory value or a data type.

Table 7.0.2.2: Overview of the data type functions 1

Table 7.0.2.3: Overview of Data Type Functions 2

The function value of SizeOf (data type) or TypeOf (expression) is one of the following constants:

Table 7.0.2.3: Overview of the function values of SizeOf (data type) and TypeOf (expression)

Hints:

• Note that TypeOf (ZERO) returns the numeric value 15 or gb. zero/.
• The function Iszero (string) returns the function value True for the following arguments:
  • string is a ZERO constant
  • string is a ZERO object reference
  • The length of string is 0
  • string represents a zero date
  • string represents an uninitialized variable of type Variant
  • list point

Gambas provides functions for converting data types. For information on these functions, see chapter 9.7 Conversion Functions.

However, Gambas also automatically converts data types. For example,“2” is a string, but can also be interpreted as an integer 2 (integer) and can be used “on the fly” after a conversion, as the following examples show:

Public Sub OnTheFly_Click()
  Print "2" + 2 ' Integer-Number
  Print "Can '2' be interpreted as an integer number? ---> ";; IsInteger("2")
  Print "Type_1 = ";; TypeOf("2" + 2) ' 7 => Float
' String + Integer
' String -> Integer => 2 + 2 = 4
  Print "2" & 2 ' String
  Print "Type_2 = ";; TypeOf("2" & 2) ' 9 => String
' String & Integer
' Integer -> String => "2" & "2" = "22"
  Print 2.1 * ("2" & 2) ' Floating-point number
  Print "Type_3 =  ";; TypeOf(2.1 * ("2" & 2)) ' 7 => Float
' Float * (String & Integer)
' Integer -> String => "2" & "2" = "22"
' Float * String => 2.1 * "22"
' String -> Float => 2.1 * 22.0 = 46.2
End ' OnTheFly()

These are the expenses in the console:

4
Can '2' be interpreted as an integer number? --->  True
Type_1 =  7
22
Type_2 =  9
46,2
Type_3 =   7