Find common area of two rectangles

rect_common_area.c

#include <stdio.h>
#include <stdlib.h>

#define inline __inline
#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))

typedef struct {
	double x, y;
} point_t;

int cmp_points_x(const point_t *p1, const point_t *p2) {
	if(p1->x > p2->x)
		return 1;
	else if(p1->x < p2->x)
		return -1;
	else {
		if(p1->y > p2->y)
			return 1;
		else if(p1->y < p2->y)
			return -1;
		else
			return 0;
	}
}
int cmp_points_y(const point_t *p1, const point_t *p2) {
	if(p1->y > p2->y)
		return 1;
	else if(p1->y < p2->y)
		return -1;
	else {
		if(p1->x > p2->x)
			return 1;
		else if(p1->x < p2->x)
			return -1;
		else
			return 0;
	}
}

inline double rect_area(const point_t *points) {
	return (points[0].x - points[3].x) * (points[0].y - points[3].y);
}

inline double d_min(double a, double b) {
	return a > b ? a : b;
}

int main(void) {
	int i;
	double area, min_area;
	point_t points[8], *pp;

	for(i = 0; i < 2; i++) {
		pp = &points[i * 4];
		//Get two points of first rectangle
		printf("\nRectangle: %i\n", i + 1);
		printf("\t%48s: ", "Base point coord (X Y)");
		scanf("%lf %lf", &pp[0].x, &pp[0].y);
		printf("\t%48s: ", "Opposite (diagonal) point coordinate (X Y)");
		scanf("%lf %lf", &pp[3].x, &pp[3].y);
		pp[1].x = pp[3].x;
		pp[1].y = pp[0].y;
		pp[2].x = pp[0].x;
		pp[2].y = pp[3].y;
	}

	min_area = d_min(rect_area(&points[0]), rect_area(&points[4]));

	qsort(points, ARRAY_SIZE(points), sizeof(points[0]), cmp_points_x);
	area = points[5].x - points[3].x;

	qsort(points, ARRAY_SIZE(points), sizeof(points[0]), cmp_points_y);
	area *= points[5].y - points[3].y;

	//TODO: better way to check if rectangles don't have common area
	if(area <= min_area)
		printf("Common area: %lf square units\n", area);
	else
		printf("No common area!\n");

	getch();

	return 0;
}