Computer Programming Concepts and Visual Basic David I. Schneider

■ RECORDS
In this text, we have worked with numbers, strings, arrays, and now fixed-length strings. Strings
and numbers are built-in data types that can be used without being declared, although we have
always elected to declare numeric and string variables using Dim statements. On the other
hand, arrays and fixed-length strings are user-defined data types that must be declared with a
Dim statement before being used. A record is a user-defined data type that groups related variables
of different types.
Figure 8-1 shows an index card that can be used to hold data about colleges. The three
pieces of data—name, state, and year founded—are called fields. Each field functions like a
variable in which information can be stored and retrieved. The length of a field is the number
of spaces allocated to it. In the case of the index card, we see that there are three fields
having lengths 30, 2, and 4, respectively. The layout of the index card can be identified by a
name, such as collegeData, called a record type.
Name: State: Year Founded:
FIGURE 8-1 An Index Card Having Three Fields
For programming purposes, the layout of the record is declared by a block of statements similar
to
Type collegeData
nom As String * 30
state As String * 2
yearFounded As Integer
End Type
User-Defined Data Types 247
Each character of a string is stored in a piece of memory known as a byte. Therefore, a
field of type String * n requires n bytes of memory. However, numbers (that is, the integer
or single-precision numbers we use in this text) are stored in a different manner than strings.
Integer numbers always use two bytes of memory, whereas single-precision numbers always
use four bytes of memory.
Visual Basic requires that Type declarations, such as the preceding record structure collegeData,
be placed in either (General) or in a special file, referred to as a BAS Module.
When placed in the (General) portion of a form, the word “Type” must be preceded by “Private”
and the record type is only valid for that form. When placed in a BAS module, the word
“Type” may be preceded by either “Private” (valid for the current BAS module) or “Public”
(valid throughout the entire program). In this text, we will primarily place our declarations
inside BAS Modules and make them Public.
To create a BAS Module for the program currently being designed, press Alt/P/M and
double-click on Module. A window like the one in Figure 8-2 will appear. This window is
where our Type declarations will be entered. To switch between this BAS Module window
and the form(s), press Ctrl+R to activate the Project Explorer and double-click on a form or