求解三角形面积（输入三个点的坐标）

#include<stdio.h>
#include<math.h>
int main() {
    int x1,y1,x2,y2,x3,y3;
    double s,a,b,c,p;
    while(scanf("%d %d %d %d %d %d",&x1,&y1,&x2,&y2,&x3,&y3)!=EOF){
        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));
        if(s==0) break;
        printf("%.1lf\n",s);
    }
    return 0;
}