1. Use __int64
2. Here is some fragment of my code(and the most significant):
   for(x=0;x<r;x++)
     k+=ceil(sqrt((double)(r-x)*(r+x))); <----- be careful!!

use binary search and the following relation: x^2+y^2=R^2

One can use Bresenham's circle algorithm to avoid all the FP calculations, but why bother if the TL is more than enough?

http://en.wikipedia.org/wiki/Midpoint_circle_algorithm

this staff is nice.
that let me deal problem.
looks like sqrt can't handle 100000*100000
also (r-x)(r+x) == r*r - x*x, but first can be handled with sqrt but second not
finally, thanks at all
sorry for bad english