1180.Echo的烦恼

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;

struct point {
    int x;
    int y;
} p[50];

double get_area(point p0, point p1, point p2) {
    int x1 = p1.x - p0.x;
    int y1 = p1.y - p0.y;
    int x2 = p2.x - p0.x;
    int y2 = p2.y - p0.y;
    return (x1 * y2 - x2 * y1) / 2.0;
}

int main(int argc, char* argv[]) {
    int n, i;
    double area;

    scanf("%d", &n);
    for (i = 0; i < n; i++)
        scanf("%d %d", &p[i].x, &p[i].y);

    for (i = 2; i < n; i++)
        area += get_area(p[0], p[i - 1], p[i]);

    printf("%.1f\n", abs(area));

    return 0;
}