题解 | 三角形面积，叉乘记得加绝对值

#include <bits/stdc++.h>
using namespace std;

struct point{
    double x,y;
    point(double A,double B){
        x=A,y=B;
    }
    point() = default;
};

struct triangle{
    point a,b,c;
    triangle(point A,point B,point C){
        a=A,b=B,c=C;
    }
    triangle() = default;
};

double getArea(triangle T){
    // TODO: 计算三角形T的面积
    return abs(0.5 * ( (T.b.x-T.a.x)*(T.c.y-T.a.y) - (T.c.x-T.a.x)*(T.b.y-T.a.y) ));
}

int main(){
    int x, y;
    cin >> x >> y;
    point a(x, y);
    cin >> x >> y;
    point b(x, y);
    cin >> x >> y;
    point c(x, y);
    triangle T(a, b, c);
    cout << fixed << setprecision(2) << getArea(T) << endl;
    return 0;
}