#include <stdio.h>

#include "genlib.h"
#include "simpio.h"

typedef struct {
	double x;
	double y;
} Point;

#define MAX 32

void getPoints(Point points[], int n);
double calculateArea(Point points[], int n);

main()
{
	Point points[MAX];
	int numOfPoints;
	
	while(TRUE) {
		printf("Posa shmeia 8elete na eisagete? ");
		numOfPoints=GetInteger();
		if ((numOfPoints > 1)&&(numOfPoints<MAX))
			break;
		printf("O ari8mos ton shmeiwn prepei na einai megalyteros h isos tou 2 ");
		printf("kai mikroteros toy 32\n");
	}


	getPoints(points, numOfPoints);

	printf("To embado ths epifaneias einai %f\n", calculateArea(points, numOfPoints));
}


/*Δημιουργία του πίνακα σημείων points*/
void getPoints(Point points[], int n)
{
	int i;

	for (i = 0; i < n; i++)
	{
		printf("x[%d]= ", i);
		points[i].x = GetReal(); 
		
		printf("y[%d]= ", i);
		points[i].y = GetReal();

		printf("\n");
	}
	
}

/*Υπολογισμός εμβαδού περιοχής*/
double calculateArea(Point points[], int n)
{
	int i;

	double area = 0.0;
	double part;
	
	for (i = 0; i < n - 1 ; i++) {
		part = (points[i].y + points[i + 1].y) * (points[i + 1].x - points[i].x) * .5;
       	area = area + part;
	}

	return area;
}