源码

#include<bits/stdc++.h>  
using namespace std;  
double x1,y1,x2,y2,x3,y3;  
int main()
{
    scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);  
    double s=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))+
    sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3))+
    sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));  
    printf("%.2lf",s);  
}

看第三行，在main函数内编译是正确的，问下大佬怎么解释