三角形面积

0 0 1 1 1 3
0 1 1 0 0 0
0 0 0 0 0 0

1.0
0.5

 
#include <iostream>
#include <string.h>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{

    int x1,y1,x2,y2,x3,y3;
    double a,b,c,p,s;
    while(cin>>x1>>y1>>x2>>y2>>x3>>y3 )
    {
        if(x1==0&&y1==0&&x2==0&&y2==0&&x3==0&&y3==0)
            break;
        else
        {
        a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
        c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
        p=(a+b+c)/2;
        s=sqrt(p*(p-a)*(p-b)*(p-c));
        cout<<fixed<<setprecision(1)<<s<<endl;

        }
    }
    
return 0;
}