初学API，执行下段代码出现：编译错误，用户定义类型末定义！

[ivbapplication]

我想完成数据的备份还原任务，就在一项目中建立了一个窗体Form1，上面放二个按BUTTON，另外一个是模块。模块中的代码为：
Public Const FO_MOVE = &H1
Public Const FO_COPY = &H2
Public Const FO_DELETE = &H3
Public Const FOF_NOCONFIRMATION = &H10
Public Const FOF_NOCONFIRMMKDIR = &H200
Public Const FOF_ALLOWUNDO = &H40
Public Const FOF_SILENT = &H4

Public Declare Function SHFileOperation Lib "shell32.dll" Alias "SHFileOperationA" (lpFileOp As SHFILEOPSTRUCT) As Long
编译时，上面一句蓝色显示，提示编译错误：用户定义类型末定义！

Form1中的窗体代码为：
'备份数据

Private Sub m_BackUp_Click()
On Error Resume Next

Dim SHFileOp As New SHFILEOPSTRUCT

SHFileOp.wFunc = FO_COPY
SHFileOp.pFrom = App.Path & "\msDATA.mdb"
SHFileOp.pTo = App.Path & "\back\msDATA.mdb"
SHFileOp.fFlags = FOF_ALLOWUNDO + FOF_NOCONFIRMMKDIR
Call SHFileOperation(SHFileOp)
MsgBox "备份已完成!"
Exit Sub

ErrHandler:
Me.MousePointer = 0

End Sub

'复原数据库
Private Sub m_restore_Click()
On Error Resume Next
Dim oldMdb As String
Dim newMdb As String
Dim SHFileOp As SHFILEOPSTRUCT
SHFileOp.wFunc = FO_COPY
SHFileOp.pFrom = App.Path & "\back\msDATA.mdb"
SHFileOp.pTo = App.Path & "\msDATA.mdb"
SHFileOp.fFlags = FOF_ALLOWUNDO + FOF_NOCONFIRMMKDIR
Call SHFileOperation(SHFileOp)
MsgBox "复原已完成!"
Exit Sub
End Sub
想知道什么是API？如何调用API？
特此询求帮助。完成任务散分。

[fvflove]

'在模块中再增加此段代码.
'因为你在API中用到了 SHFILEOPSTRUCT 结构.
Public Type SHFILEOPSTRUCT
        hwnd As Long
        wFunc As Long
        pFrom As String
        pTo As String
        fFlags As Integer
        fAnyOperationsAborted As Long
        hNameMappings As Long
        lpszProgressTitle As String '  only used if FOF_SIMPLEPROGRESS
End Type

'Application Programming Interface 应用编程接口 || 简称 API

[ivbapplication]

简练明了，一步到位。搞定！多谢侠女指点。
散分了。