Character code input/output

• get_code(Stream,Code):   Inputs a byte from Stream and unifies Code with the byte. After reaching the end of file, it unifies Code with -1.

• get_code(Code):   The same as the previous one except that the current input stream is used.

• peek_code(Stream,Code):   The current code in Stream is Code. The postion pointer of Stream remains the same after this operation.

• peek_code(Code):   The same as
• peek_code(Stream,Code) except that the current input stream is used.

• put_code(Stream,Code):   Outputs a byte Code to the stream Stream.

• put_code(Code):   Outputs a byte Code to the current output stream.