points.c

凸多边形面积凸多边形面积凸多边形面积凸多边形面积凸多边形面积凸多边形面积凸多边形面积凸多边形面积凸多边形面积

#include <stdio.h>
#define MAX_LINE_N 15

int main()
{
	double point[MAX_LINE_N+1][2]={0,0};
	int i=0, j=0;
	double area=0.0;
	//get x and y from stdin
	while(scanf("%lf%lf", &point[i][0], &point[i][1]) != EOF)
		i++;
	//copy the first point to the position behind the last point
	point[i][0] = point[0][0];
	point[i][1] = point[0][1];
	//compute the area of polygon by dividing it into several trapezoids
	for (j=0; j<i; j++)
		area += (point[j][1] - point[j+1][1]) * (point[j][0] + point[j+1][0]) / 2;
	//print the area retaining two decimal
	printf("%.2f", area);
	return 0;
}