http://acm.hdu.edu.cn/showproblem.php?pid=2001
1 /*written by czk*/ 2 #include <stdio.h> 3 #include <math.h> 4 5 int main() { 6 double x1, y1, x2, y2; 7 while(scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2) != EOF) 8 printf("%.2f\n", sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2))); 9 }