integer division in Ruby with negative value -


trying negative value division in ruby, e.g. -123/10, why returns -13 instead of -12 ?

ruby -v ruby 1.9.3p375 (2013-01-18) [x86_64-darwin12.2.1]  irb(main):001:0> -123/10 => -13 irb(main):002:0> -123%10 => 7

-123/10 returns -12 , -123%10 returns -3 in c/c++ expected.

this how designed. ruby rounds numbers towards negative infinity in case of negative division , modulo operation. not unique ruby, python , perl behaves also.

however, approach provides mathematical reason.

a / b = q remainder r

such that

b * q + r = , 0 <= r < b

from read, how arithmetic taught in japan.

edit:

sawa pointed out how positive arithmetic taught in japan, not negative numbers. however, said, can extended negative numbers well.

sources:

ruby forums


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