1.建立用户表  user.dbf (username c (8) , password (30))
2.表立表单 load  数据环境为user.dbf
    2.a. 为表单添加 label1,label2,combo1,text1,command1,command2
    2.b. 表单 的init
         publ nNumber,cUsername
         nNumber = 0
         表单的 unload
         cUsername = 表1.username
         thisform.combo1.vlaue = 1
    2.c. label1 .caption = "用户名："
      d. label2.caption = "口  令："
      e. combo1.ControlSource = user.username
      f. text1.PasswordChar = "*"
      g. command1.caption = "确定(\<E)"
      h. command2.caption = "取消(\<C)"
      i. command1.click  
               if nNumber > 2 
                     messagebox("你输入 的密码大于三次！",'系统提示')
                     clear events
                     quit 
               endif
               select user.dbf
               loca for allt(user.password)==allt(thisform.text1.value)
               if !eof()
                   messagebox("欢迎使用本系统",'系统提示')
                   do XXXX.mpr
                   thisform.releae
               else
                   messagebox("口令错误！",48,"系统提示")
                   nNumber = nNumber + 1
               endif
      j. command2.click 
               thisform.release