我用 《iostream》 过了，用《cstdio》测试点5没过，想不清楚为什么，请大佬帮忙！```cpp

#include #include #include using namespace std; double dis(double x1,double x2,double y1,double y2) { double ans; ans=sqrt(pow((x2-x1),2)+pow((y2-y1),2)); return ans; } int main() { double x1,x2,x3,y1,y2,y3; double answer; cin>>x1>>y1>>x2>>y2>>x3>>y3; answer=dis(x1,x2,y1,y2)+dis(x1,x3,y1,y3)+dis(x2,x3,y2,y3); cout<<fixed<<setprecision(2)<<answer; return 0; }

```cpp
#include <cstdio>
#include <cmath>
using namespace std;
double dis(double x1,double x2,double y1,double y2)
{
	double ans;
	ans=sqrt(pow((x2-x1),2)+pow((y2-y1),2));
	return ans;
}
int main()
{
	double x1,x2,x3,y1,y2,y3;
	double answer;
	scanf("%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
	answer=dis(x1,x2,y1,y2)+dis(x1,x3,y1,y3)+dis(x2,x3,y2,y3);
	printf("%.2lf",answer);
	return 0;
}