$INCR
: Increment a macro
$INCR(
N)
redefines the numeric macro N to be one greater
than its previous value. (If N does not simplify to a number, an
error results.) In other words, in the language of C the effect is to
say N
++
.
The two-argument form $INCR(
N,m)
executes the equivalent of
N
+=
m.