#include<stdio.h>
#include<math.h>
int main()
{
double x1,y1,x2,y2,l,a;
while(scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2)!=EOF)
{
a=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
l=pow(a,0.5);
printf("%.2lf\n",l);
}
}
原文：http://www.cnblogs.com/woderenshengluwozijizou/p/4442664.html