什么是好的代码，好的代码不是简单的可以运行，而应该是简洁美观的，让人很容易就可以看懂的，所以我们在使用循环的时候应尽可能的减少循环的层数。

比较下面两段代码：

代码1：

    If Trim(txtUserName.Text = "") Then
        MsgBox "没有这个用户，请重新输入！",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 = True Then
            MsgBox "没有这个用户，请重新输入！","警告"
            txtUserName.SetFocus
        Else
            If Trim(mrc.Fields(1)) <> Trim(txtPassword.Text) Then
                MsgBox "密码错误，请重新输入！","警告"
                txtPassword.SetFocus
                txtPassword.Text = ""
            Else
                OK = True
                mrc.Close
                Me.Hide
                UserName = Trim(txtUserName.Text)
            End If
        End If
    End If

代码2：

    If Trim(txtUserName.Text = "") Then
        MsgBox "请输入用户名！","警告"
        txtUserName.SetFocus
        Exit Sub
    End If
    
    txtsql = "select * from User_Info where userID= '" & txtUserName.Text & "'"
    Set mrc = Executesql(txtsql,MsgText)

    If mrc.EOF = True Then
        MsgBox "没有这个用户，请重新输入！","警告"
        txtUserName.SetFocus
        Exit Sub
    End If
        
    If Trim(mrc.Fields(1)) <> Trim(txtPassword.Text) Then
        MsgBox "密码错误，请重新输入！","警告"
        txtPassword.SetFocus
        txtPassword.Text = ""
        Exit Sub
    End If
            
    OK = True
    mrc.Close
    Me.Hide
    UserName = Trim(txtUserName.Text)

初学者，不当之处敬请评指正！

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