On Tue, Dec 13, 2011 at 2:55 AM, Nick Dokos <nicholas.do...@hp.com> wrote: > Terry Reedy <tjre...@udel.edu> wrote: >> calculations are helped by the fact that (a+b) % c == a%c + b%c, so > > As long as we understand that == here does not mean "equal", only > "congruent modulo c", e.g try a = 13, b = 12, c = 7.
This is the basis of the grade-school "casting out nines" method of checking arithmetic. Set c=9 and you can calculate N%c fairly readily (digit sum - I'm assuming here that the arithmetic is being done in decimal); the sum of the remainders should equal the remainder of the sum, but there's the inherent assumption that if the remainders sum to something greater than nine, you digit-sum it to get the true remainder. (Technically the sum of the digits of a base-10 number is not the same as that number mod 9, but if you accept that 0 == 9, it works fine.) ChrisA -- http://mail.python.org/mailman/listinfo/python-list
