itsa [C_MM067-易]三角形面積

#include<iostream>
#include<iomanip>
using namespace std;

int main()
{
int A, B, C, D;
cin >> A >> B;
cin >> C >> D;

int x, y;
long double m, a, c;
x = A;           
y = B;
m = (1.0 * (D - B)) / (C - A);
c = y - m * x;

int x1, y2;
long double y1, x2;
x1 = 0; 
y1 = c;
y2 = 0;
x2 = -c / m;
if (x2 < 0)
{
x2 = -x2;
}
if (y1 < 0)
{
y1 = -y1;
}
a = (x2 * y1) / 2;
cout << fixed << setprecision(5) << a << endl;
return 0;
}