Visual Basic/Data Types
Datatypes in Visual Basic can be divided into three groups:
- those types that are understood directly by the Visual Basic compiler without assistance from the programmer,
- user defined
- commonly referred to by the initials UDT, meaning User defined Type, these correspond to Pascal records or C structs,
- these are the basis for object oriented programming in Visual Basic. Note that forms and the various Add-inn and database designers are also classes.
Built in Types
The built in types are:
- 8 bit, unsigned
- 16 bit, signed
- 32 bit signed
- 32 bit floating point, range about
- 64 bit IEEE floating point, range about
- exact representation of decimal numbers of up to four decimal places
- dynamically allocated UniCode strings, theorectical capacity about characters.
- an associative array of Variants.
- 8 byte date/time value range January 1, 100 to December 31, 9999
- a holder for any type of Object.
- a holder for any type of value or object.
Byte, Integer & Long
Dim a as Byte Dim i as Integer Dim x,y as Long 'Define two variables. Note that only the last variable will be a long integer.
Now those variables will only be capable of storing integer values (without decimal). Long integers can store a number with a bigger range of value than integers but they occupy a bigger space of RAM.
|Type||Storage||Range of Values|
|Byte||1 byte||0 to 255|
|Integer||2 bytes||-32,768 to 32,767|
|Long||4 bytes||-2,147,483,648 to 2,147,483,647|
Some functions you need to know: Int()
Int() converts a decimal value into an integer value:
Dim i as Integer i=Int(3.9) Print i
Single & Double
These data types can store decimal values. "Double" compared to "Single" is similar to the "Long" compared to "Integer":
|Type||Storage||Range of Values|
|Single||4 bytes||-3.402823E+38 to -1.401298E-45 for negative values
1.401298E-45 to 3.402823E+38 for positive values.
|Double||8 bytes||-1.79769313486232e+308 to -4.94065645841247E-324 for negative values
4.94065645841247E-324 to 1.79769313486232e+308 for positive values.
Some useful functions: Round()
Round() rounds off a decimal to a certain number of decimal digits that the programmer wants. The first argument should be a decimal value which you want to round off. The second argument specifies the number of decimal digits you want, for example:
Dim pi as Double pi=3.141592653589 pi=Round(pi,2) 'Rounds off 3.141592653589 to only two decimal digits Print pi
A string is an array of characters. As an example:
Dim a As String a = "This is a string"
Strings can be concatenated (connected together to form a new string) using the "&" operator. For example,
dim b as String b = "Wiki" & "book" & "s" Print b
A normal string variable occupies 10 bytes of RAM, plus the string's size, and can hold up to 2 billion characters!
Some frequently used built-in string constants: vbTab, vbCrLf
vbTab contains a string that does the same thing as the Tab key on your keyboard, while vbCrLf creates a character return and a line feed(similar to the Enter key):
Print "Jack:" & vbTab & "1 pie" & vbCrLf & "me:" & vbTab & "10 pies"
Jack: 1 pie me: 10 pies
To include special characters and quotation marks in the strings, the Chr() function may be used:
Dim a As String Print "A quotation mark: [" & Chr(34) & "]" a = "Replace 'apostrophes' for quotation marks" Replace( a, "'", Chr(34) ) Print a
Some string functions: Str(),Val(),inStr(),Mid(),Replace(),Trim()
In fact there are tons of built-in string manipulation functions available. But right now, I'll just introduce two: Str() and Val().
Str() converts any numerical value into a string value while Val() converts a string value into a numerical value(only when it's convertible).
Dim MyString As String Dim MyNumber As Single MyString=Str(300) 'converts a number into a string MyNumber=Val("300") 'converts a string into a number
Even if you don't do the conversion, you will not end up getting Type Mismatch Errors. However, it is considered better to use explicit type conversions, because it is easier to debug.
Even if you do be prepared for next to impossible to debug problems caused by VB refusing to convert something and refusing to tell you what the heck it is. VB is extremely touchy and raises an exception at the least expected times.
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