计算两点间的距离

#include<stdio.h>
#include<math.h>
int main( )
{
 double x1,y1,x2,y2;
 while(scanf("%lf",&x1)!=EOF)
 {
  scanf("%lf%lf%lf",&y1,&x2,&y2);
  printf("%.2lf\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
}
return 0;
}