Programming Excel with VBA and .NET

Declarations

Visual Basic has automatic variables by default. That means a new variable is created the first time you use it. This makes life somewhat easier for beginning programmers, but it makes things harder when writing and maintaining complex programs. For that reason, most experts recommend that you require variable declarations by adding Option Explicit to the beginning of each class or module.

Option Explict turns off Visual Basic’s automatic variables and thus requires that you declare each variable before you use it. To declare a variable, use the Dim statement:

    Dim x As Integer

The preceding code declares that the name x is a variable that can contain an integer. The 12 different types of variables in Visual Basic are listed in Table 2-3.

Table 2-3. Data types for variables in Visual Basic

Type	Kind of data	Size	Values
Boolean	True/false choices	2 bytes	True (0), False (-1)
Byte	Binary data	1 byte	0-255
Currency	Monetary values	8 bytes	−922,337,203,685,477.5808 to 922,337,203,685,477.5807
Date	A date or time	8 bytes	1 January 100 to 31 December 9999
Double	Large decimal numbers	8 bytes	1.79769313486231E308 to −4.94065645841247E-324 for negative values and from 4.94065645841247E-324 to 1.79769313486232E308 for positive values
Integer	Whole numbers	2 bytes	−32,768 to 32,767
Long	Large whole numbers	4 bytes	−2,147,483,648 to 2,147,483,647
Object	An instance of a class	4 bytes	Address of the object in memory
Single