@dave Nice explanation!
Yanan Cao On Tue, Aug 21, 2012 at 10:32 AM, Dave <dave_and_da...@juno.com> wrote: > @Wladimirufc: You responded that the type is int. This data type (usually) > is 32 bits in length, and stores integers in the twos-complement number > system. See http://en.wikipedia.org/wiki/Two%27s_complement for an > explanation of this number system. In this number system, the bits > (numbered 0 to 31 from the right) have values 2^i (2 to the ith power) for > i = 0, 1, ..., 30, while bit 31 has value -2^31. > > In your code, you set x to have a 1-bit in bit 31 and zeros elsewhere. > Thus, the value of x is -2^31, which is the value printed by the first > printf() statement. This value is negative, so the value is negated. In > twos-complement arithmetic, a value is negated by complementing the value > (switching 0s to 1s and 1s to 0s) and then adding 1. I.e., the statement x > = -x is functionally equivalent to x = (~x) + 1. For your value of x, the > resulting value is the same as the original value, so the second printf() > statement also prints the value -2^31. > > I'm glad you asked this question because it is very important to > understand how quantities are stored in C and how the arithmetic works. > > Dave > > On Tuesday, August 21, 2012 11:25:11 AM UTC-5, wladimirufc wrote: > >> Somebody could explain to me why this happen: >> x = (1<<31); >> printf("%d\n",x); >> if(x<0) x = -x; >> printf("%d\n",x); >> >> Output: >> >> -2147483648 >> -2147483648 >> >> Wladimir Araujo Tavares >> *Federal University of Ceará <http://lia.ufc.br/%7Ewladimir/> >> Homepage <http://lia.ufc.br/%7Ewladimir/> | >> Maratona<https://sites.google.com/site/quixadamaratona/>| >> * >> >> >> > -- > You received this message because you are subscribed to the Google Groups > "Algorithm Geeks" group. > To view this discussion on the web visit > https://groups.google.com/d/msg/algogeeks/-/7a3Wer6PRRQJ. > > To post to this group, send email to algogeeks@googlegroups.com. > To unsubscribe from this group, send email to > algogeeks+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/algogeeks?hl=en. > -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
