Closing Sequential I/O Files
Each I/O file that is opened should be closed when you have finished reading from or writing to it. Closing the file releases the channel for use with another I/O operation. It also makes the file available to be accessed by some other process.
Syntax for Closing Files
Closing an Input File
Close_Input [channel {channel-num.}]
Closing an Output File
Close_Output [channel {channel-num.}]
Parameters
{channel-num.}: The assigned channel of the file that is being closed. If the channel parameter is omitted, then the default input or output channels will be closed.