#include<bits/stdc++.h>
using namespace std;
double x1,y1,x2,y2,x3,y3;
double s(double n){
    return n>0?n:-n;
}
int main(){
    cin>>x1>>y1>>x2>>y2>>x3>>y3;
    cout<<s((x1-x3)*(y1-y3)-(x2-x3)*(y2-y3))/2;
    return 0;
}

报错显示：

/tmp/compiler_jx1wp0ot/src:3:11: 错误：‘double y1’被重新声明为不同意义的符号double x1,y1,x2,y2,x3,y3;**

验证mzbf祭