1372Problem B:几何题（一）

#include<stdio.h>
//  作者： 许同学 
double direction( double x1,double y1,double x2,double y2,double x0,double y0 )   //直线方向是由(x1,y1)到(x2,y2)的方向
{
    double a,b,c,d;
    a=y2-y1;
    b=x1-x2;
    c=x2*y1-x1*y2;
    d=a*x0+b*y0+c;
    return d;           //若d<0，则点P在直线的左侧,若d>0，则点P在直线的右侧,若d＝0，则点P在直线上
}
int main()
{
    int t;
    double x1,y1,x2,y2,x3,y3,x4,y4,x0,y0;
    double a1,a2,a3,a4;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf %lf %lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4,&x0,&y0);
        a1=direction( x1,y1,x2,y2,x0,y0 );
        a2=direction( x2,y2,x3,y3,x0,y0 );
        a3=direction( x3,y3,x4,y4,x0,y0 );
        a4=direction( x4,y4,x1,y1,x0,y0);
        if(a1<0&&a2<0&&a3<0&&a4<0 ||a1>0&&a2>0&&a3>0&&a4>0 )
           printf("T\n");
        else
           printf("F\n");
    }
    return 0;
}