nyoj-67-三角形面积(S=(1/2)*(x1y2+x2y3+x3y1-x1y3-x2y1-x3y2))

题目链接

 /*
     Name:nyoj-67-三角形面积
     Copyright:
     Author:
     Date: 2018/4/26 16:44:47
     Description:
     三角形的三个顶点坐标求其面积的公式为:
         S=(1/2)*(x1y2+x2y3+x3y1-x1y3-x2y1-x3y2)
 */
 #include <iostream>
 #include <cstdio>
 using namespace std;
 int main()
 {
     int x1,x2,x3,y1,y2,y3;
     while (cin>>x1>>y1>>x2>>y2>>x3>>y3, x1+x2+x3+y1+y2+y3) {
         double ans = x1*y2 + x2*y3 + x3*y1 -x1*y3 - x2*y1 - x3*y2;
         printf("%.1f\n", ans/>?ans/:-ans/);
     }
     return ;
 }