# Structures and Other Programming Elements (Visual Basic)

You can use structures in conjunction with arrays, objects, and procedures, as well as with each other. The interactions use the same syntax as these elements use individually.

Note

You cannot initialize any of the structure elements in the structure declaration. You can assign values only to elements of a variable that has been declared to be of a structure type.

## Structures and Arrays

A structure can contain an array as one or more of its elements. The following example illustrates this.

Public Structure systemInfo
Public cPU As String
Public memory As Long
Public diskDrives() As String
Public purchaseDate As Date
End Structure


You access the values of an array within a structure the same way you access a property on an object. The following example illustrates this.

Dim mySystem As systemInfo
ReDim mySystem.diskDrives(3)
mySystem.diskDrives(0) = "1.44 MB"


You can also declare an array of structures. The following example illustrates this.

Dim allSystems(100) As systemInfo


You follow the same rules to access the components of this data architecture. The following example illustrates this.

ReDim allSystems(5).diskDrives(3)
allSystems(5).CPU = "386SX"
allSystems(5).diskDrives(2) = "100M SCSI"


## Structures and Objects

A structure can contain an object as one or more of its elements. The following example illustrates this.

Protected Structure userInput
Public inputForm As System.Windows.Forms.Form
Public userFileNumber As Integer
End Structure


You should use a specific object class in such a declaration, rather than Object.

## Structures and Procedures

You can pass a structure as a procedure argument. The following example illustrates this.

Public currentCPUName As String = "700MHz Pentium compatible"
Public currentMemorySize As Long = 256
Public Sub fillSystem(ByRef someSystem As systemInfo)
someSystem.cPU = currentCPUName
someSystem.memory = currentMemorySize
someSystem.purchaseDate = Now
End Sub


The preceding example passes the structure by reference, which allows the procedure to modify its elements so that the changes take effect in the calling code. If you want to protect a structure against such modification, pass it by value.

You can also return a structure from a Function procedure. The following example illustrates this.

Dim allSystems(100) As systemInfo
Function findByDate(ByVal searchDate As Date) As systemInfo
Dim i As Integer
For i = 1 To 100
If allSystems(i).purchaseDate = searchDate Then Return allSystems(i)
Next i
End Function


## Structures Within Structures

Structures can contain other structures. The following example illustrates this.

Public Structure driveInfo
Public type As String
Public size As Long
End Structure
Public Structure systemInfo
Public cPU As String
Public memory As Long
Public diskDrives() As driveInfo
Public purchaseDate As Date
End Structure

Dim allSystems(100) As systemInfo
ReDim allSystems(1).diskDrives(3)
allSystems(1).diskDrives(0).type = "Floppy"


You can also use this technique to encapsulate a structure defined in one module within a structure defined in a different module.

Structures can contain other structures to an arbitrary depth.