OPEN file$ [FOR mode] [ACCESS access] [lock] AS [#]filenumber% [LEN=reclen%]  
OPEN database$ FOR ISAM tabletype tablename$ AS [#]filenumber%                
                                                                              
    ■ file$          文件名称或者路径
    ■ mode        Random 随机║ Binary 二进制   ║ Input  输入   ║ Output 输出║ Append    追加    
    ■ access       Read 读  ║ Write  写   ║ Read Write     读写                     
    ■ lock           Shared 数据共享║ Lock Read 独占模式读入║ Lock Write ║ Lock Read Write        
    ■ filenumber%    An integer expression with a value between 1 and 255.    一个1到255之间的整数
    ■ reclen%        Random-access files:   The record length.                随即存取的记录长度
                     Sequential files:      The number of characters buffered.顺序文件字符缓冲数
    ■ database$      A database filename or path.          一个数据文件名或者路径                    
    ■ tabletype      The name of a type of table defined using TYPE.      TYPE定义的表的类型
    ■ tablename$     Follows the ◄ISAM Naming Conventions►.            

DIM Filenum AS INTEGER
CLS
INPUT "Enter file name: ", filename$
Filenum% = FREEFILE
OPEN filename$ FOR OUTPUT AS Filenum%
PRINT : PRINT UCASE$(filename$); " opened for output as File #"; Filenum%
'Put something in the file.
PRINT #Filenum%, "The quick brown fox jumped over the lazy yellow dog."
'Close the file.
CLOSE Filenum%

Filenum% = FREEFILE
OPEN filename$ FOR INPUT AS Filenum%
PRINT : PRINT UCASE$(filename$); " has been reopened for input."
LINE INPUT #Filenum%, L$
PRINT : PRINT "The contents of the file are:"; L$
CLOSE Filenum%
'Remove the file from disk.
KILL filename$

谢谢1楼的！！！
不过我还是有的“糊涂”：

OPEN file$ [FOR mode] [ACCESS access] [lock] AS [#]filenumber% [LEN=reclen%]

参数中的‘[ ]’是可选项吗？？

OPEN "I", #1, DA$
这和函数原形怎么对起来，你没帮我解释一下啊？？？！！！
希望继续帮忙啊！！！

楼上的好资料，得好好顶一下[em9]

OPEN file$ [FOR mode] [ACCESS access] [lock] AS [#]filenumber% [LEN=reclen%]

参数中的‘[ ]’是可选参数。

“OPEN "I", #1, DA$”这条语句有问题吧
中间的逗号
OPEN "I" AS #1 DA$一样不对
程序自动添加OPEN "I" FOR RANDOM AS #1 DA$
这里DA$会报错。因为后面应该是一个随机存取的长度修改为
OPEN "I" FOR RANDOM AS #1 LEN=3

哦。。
谢谢。。
我自己再去调试调试！！！

OPEN可以这样用:
OPEN "F:\编程\3z.in" FOR INPUT AS #1
其中OPEN、"、:、\、"、FOR、AS、#1不要动，INPUT还可以改成ouput.