Commodore Plus 4 - Controlling colors

86 The BASIC Language
and the file is flagged as SCRATCHed in the disk directory. The number of
blocks occupied by the SCRATCHed file are freed for use.
Once overwritten, SCRATCHed files are lost permanently from the disk.
When you issue a SCRATCH command in immediate mode, the computer gives
you a chance to double check before the command is executed. The question
ARE YOU SURE ? is displayed, and the computer does not proceed with the
SCRATCH operation until you respond. Type Y to proceed. If you type anything
else, the SCRATCH operation is aborted. In program mode, the question is not
asked.
After you SCRATCH a file, you can verify that the file is deleted by displaying
the disk directory. Note the difference in total blocks free now that the file is
SCRATCHed.
Note: If a file is inadvertently SCRATCHed, it can sometimes be recovered
using direct-access disk commands. See Chapter 6 for a sample program.
Parameters: "file name", D drive number, U unit number
1. Include the name of the file you want to SCRATCH. The name must be in
quotes. It may contain wild cards, but take care to SCRATCH only files you no
longer need. You can check which files would be deleted before you execute the
SCRATCH by using the DIRECTORY command with the same file name
parameter.
2. Drive numbers are either 0 or 1. No other numbers are allowed. You can
omit this parameter if you are using a single disk drive, or if you are scratching a
file in drive 0 of a dual drive.
3. Unit number is an optional parameter. Use it only if more than one disk
drive is connected to your computer and you are using a device other than unit 8
in the SCRATCH procedure. You must precede the unit number with U, and the
unit number must be between 8 and 11. You can also type ON before U, but ON is
never required.
Note: The drive and unit number parameters and the file name can be speci
fied with a variable or expression in parentheses.
Examples: SCEATCH "GAME", Dl Removes file GAME from the disk in drive 1 of
a dual drive.
SCRATCH "PICKNUM" Scratches file PICKNUM.
SGN Abbr. sG
SGN (number)
Finds the sign—positive, negative, or zero—of the number. PRINT SGN(X)
displays one of the following three responses: