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

 1 /*
 2     Name:nyoj-67-三角形面积
 3     Copyright:
 4     Author:
 5     Date: 2018/4/26 16:44:47
 6     Description:
 7     三角形的三个顶点坐标求其面积的公式为: 
 8         S=(1/2)*(x1y2+x2y3+x3y1-x1y3-x2y1-x3y2)
 9 */
10 #include <iostream>
11 #include <cstdio>
12 using namespace std;
13 int main()
14 {
15     int x1,x2,x3,y1,y2,y3;
16     while (cin>>x1>>y1>>x2>>y2>>x3>>y3, x1+x2+x3+y1+y2+y3) {
17         double ans = x1*y2 + x2*y3 + x3*y1 -x1*y3 - x2*y1 - x3*y2;
18         printf("%.1f\n", ans/2>0?ans/2:-ans/2);
19     }
20     return 0;
21 }