⎕FC Format Control

The system variable ⎕FC contains six characters used by the primitive format function ⍕. The characters are used as follows:

       Character    Default          Usage
           1          .              Decimal point character
           2          ,              Thousands indicator
           3          *              Fill for blanks
           4          0              Fill  for overflows (the default 0  causes a
                                     DOMAIN ERROR)
           5          _              Print as blank (cannot be ,.0123456789)
           6          ¯              Negative number indicator

For details of the way in which ⎕FC is used, see the entries for ⍕ (Format by Specification and Format by example).