frmdivide.frm

Visual Basic 6 大学教程的代码

VERSION 5.00
Begin VB.Form frmDivide 
   Caption         =   "Fig. 13.3: Divide By Zero"
   ClientHeight    =   2145
   ClientLeft      =   3135
   ClientTop       =   1860
   ClientWidth     =   3510
   LinkTopic       =   "Form1"
   ScaleHeight     =   2145
   ScaleWidth      =   3510
   Begin VB.TextBox txtInput 
      Height          =   375
      Index           =   0
      Left            =   1800
      TabIndex        =   0
      Top             =   240
      Width           =   1215
   End
   Begin VB.TextBox txtInput 
      Height          =   375
      Index           =   1
      Left            =   1800
      TabIndex        =   3
      Top             =   720
      Width           =   1215
   End
   Begin VB.Label lblResult 
      Alignment       =   2  'Center
      BorderStyle     =   1  'Fixed Single
      Height          =   375
      Left            =   240
      TabIndex        =   4
      Top             =   1440
      Width           =   2775
   End
   Begin VB.Label lblPrompt 
      Caption         =   "Enter Denominator:"
      Height          =   255
      Index           =   1
      Left            =   240
      TabIndex        =   2
      Top             =   720
      Width           =   1455
   End
   Begin VB.Label lblPrompt 
      Caption         =   "Enter Numerator:"
      Height          =   255
      Index           =   0
      Left            =   240
      TabIndex        =   1
      Top             =   240
      Width           =   1335
   End
End
Attribute VB_Name = "frmDivide"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
' Fig. 13.3
' Divide by zero error handling program
Option Explicit          ' General declaration

Private Sub lblResult_Click()
   Dim numerator As Double
   Dim denominator As Double
 
   On Error GoTo inputHandler
      numerator = txtInput(0).Text
      denominator = txtInput(1).Text
      
      ' Nested On Error statement
      On Error GoTo divideByZeroHandler
         lblResult.Caption = "Result is " & _
                             numerator / denominator

      Exit Sub    ' Prevents error handler from being executed
                  ' if an error is not raised
               
divideByZeroHandler:           ' Label for error handler
   lblResult.Caption = "Attempted divide by zero!"
   Exit Sub       ' Prevent next handler from executing

inputHandler:
   lblResult.Caption = "Attempted non-numeric input!"

End Sub

Private Sub txtInput_GotFocus(Index As Integer)
   lblResult.Caption = "Click Here to Perform Division"
   txtInput(Index).Text = ""   ' Clear TextBox with focus
End Sub