学生信息管理系统优化（一）【限制字符，限制输入密码次数】

1.提示三次输入错误密码，自动退出程序

Private Sub cmdOK_Click()
    Dim txtSQL As String
    Dim mrc As ADODB.Recordset
    Dim MsgText As String

    
    UserName = ""
    If Trim(txtUserName.Text = "") Then
        MsgBox "没有这个用户，请重新输入用户名！", vbOKOnly + vbExclamation, "警告"
        txtUserName.SetFocus
    Else
    txtSQL = "select * from user_Info where user_ID = '" & txtUserName.Text & "'"
    Set mrc = ExecuteSQL(txtSQL, MsgText)
        If mrc.EOF Then
            miCount = miCount + 1
            If miCount = 1 Then
                MsgBox "用户名错误，您还有两次机会!", vbOKOnly + vbExclamation, "警告"
                txtUserName.SetFocus
                Exit Sub
            End If
             
            If miCount = 2 Then
               MsgBox "用户名错误，您还有一次机会!", vbOKOnly + vbExclamation, "警告"
               txtUserName.SetFocus
               Exit Sub
            End If
                 
            If miCount = 3 Then
               MsgBox "用户名错误，即将退出系统!", vbOKOnly + vbExclamation, "警告"
               End
            End If
        Else
            If Trim(mrc.Fields(1)) = Trim(txtPassWord.Text) Then
                OK = True
                mrc.Close
                Me.Hide
                UserName = Trim(txtUserName.Text)
                FrmMain.Show
            Else
                miCount = miCount + 1
                If miCount = 1 Then
                    MsgBox "密码错误，您还有两次机会!", vbOKOnly + vbExclamation, "警告"
                    txtPassWord.SetFocus
                    Exit Sub
                End If
             
                If miCount = 2 Then
                   MsgBox "密码错误，您还有一次机会!", vbOKOnly + vbExclamation, "警告"
                   txtPassWord.SetFocus
                   Exit Sub
                End If
                     
                If miCount = 3 Then
                   MsgBox "密码错误，即将退出系统!", vbOKOnly + vbExclamation, "警告"
                   End
                End If

            End If
        End If
    End If 
    
    
End Sub

**

2.修改各个文本框的输入字符的长度

**
通过修改属性的中的Maxlengh来实现

3.所有的姓名文本框均要限制只能添加汉字

实现代码：

Private Sub txtSID_KeyPress(KeyAscii As Integer)

Select Case KeyAscii 
Case Is < 0, &H20, &H8 
Case Else 
KeyAscii = 0 
MsgBox “姓名只能输入汉字” 
End Select 
End Sub

4.所有班号，教室，成绩，电话都限制只能添加数字

If KeyAscii >= 48 And KeyAscii <= 57 Or KeyAscii = 8 Then
    Else
       KeyAscii = 0
       MsgBox "只能输入数字！"
    End If

5.限制输入非法字符

实现代码：

  If ((KeyAscii >= 48 And KeyAscii <= 57) Or (KeyAscii >= 65 And KeyAscii <= 90) Or _
      (KeyAscii >= 97 And KeyAscii <= 122) Or (KeyAscii = 8)) = False Then
      KeyAscii = 0
      MsgBox "禁止输入非法字符！", vbOKOnly, "警告"
  End If