#include <stdio.h>
#include <math.h>
double areas(double x1, double y1, double x2, double y2, double x3, double y3) {
    /*計算三邊長度*/
    double a = sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
    double b = sqrt(pow(x2 - x3, 2) + pow(y2 - y3, 2));
    double c = sqrt(pow(x3 - x1, 2) + pow(y3 - y1, 2));
    /*海倫公式*/
    double p = (a + b + c) / 2.0;
    double s = sqrt(p*(p-a)*(p-b)*(p-c));
    return s;
}

int main() {
    int n;
    double arr[300];
    int i;
    double s;
    while (scanf("%d", &n)!=EOF) {
        if (n == 0) {
            break;
        }
        s = 0;
        for (i = 0; i < n * 2; i++) {
            scanf("%lf", &arr[i]);
        }
        arr[i] = arr[0];
        arr[i+1] = arr[1];
        for (i = 0; i < n * 2; i+=4) {
            s += areas(arr[i] ,arr[i + 1], arr[i + 2], arr[i + 3], arr[i + 4], arr[i + 5]);
        }
        printf("%.1lfn", s);
    }
    return 0;
}
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Followed by:

• Re:為何海倫公式不行？樣例能過，也帶了兩個凹多邊形也是對的，所以錯在哪里了？或者求人給反例數據，謝謝 (1032)  NIOT2018_江堤楓 2018-06-12 22:01:12 Problem 2036

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