UNDEFVARMOD

Message        <Context> the expression "<expr>" modifies the
               variable "<var>" more than once without an
               intervening sequence point.  This behavior is
               undefined.

Description    The compiler has detected a case where the same
               variable has been modified more than once in an
               expression without a sequence point between the
               modifications.  Because what modification will occur
               last is not defined, this expression might produce
               different results on different platforms.

User Action    Rewrite the expression so that each variable is
               modified only once.