Understanding Data Types
Okay, you know what a variable does and how to name it. But what can you store in a variable? The simple answer is: almost anything. A variable can hold a numeric value; a string of text; or a reference to an object, such as a form, control, or database. This chapter looks specifically at using variables to store numbers, strings, and dates. Table 6.2 lists Visual Basic’s data types:
| Visual Basic .NET Data Type | Values Stored | Example | Memory Requirements |
|---|---|---|---|
| Boolean | True/False | True | 2 bytes |
| Byte | 0–255 | 122 | 1 byte |
| Char | Single Character | A | 2 bytes |
| Date | Dates and Times | 12/21/1970 02:00 PM | 8 bytes |
| Decimal | Decimal or Whole | 19.95D | 16 bytes |
| Double | Decimal Numbers | 1.23E-10 | 8 bytes |
| Integer | Whole Numbers | 8675309 | 4 bytes |
| Long | Whole Numbers | 19-digit number | 8 bytes |
| Object | A reference to an object of any type | 4 bytes | |
| Short | Whole Numbers | 32,123 | 2 bytes |
| Single | Decimal Numbers | .0000123 | 4 bytes |
| String | Characters | HELLO | Depends on length |
Note
The little Integer from VB 6.0 has finally grown up! A Visual Basic .NET Integer variable can store the entire range of values of a Visual Basic 6.0 Long variable. (This brings a welcome level of consistency to those programmers who work with the int type in SQL databases.) A new type, the Short type, takes the place of the VB6 Integer with a range of -32,768 to +32,767.
Note
The Currency data type from earlier versions of Visual Basic has been eliminated. The help files suggest using the new Decimal data type as a replacement.
Note
The Variant data type, capable of storing any other variable type, has been eliminated. Because all of the base data types derive from the Object class, Microsoft has named Object as the new universal data type.
In Visual Basic .NET, even the most basic data types act like objects, with their own properties and methods. When you type a variable name in the Code Editor and press the period key, you will see all the associated methods and properties.