#include <stdio.h>
#include <math.h>

struct Point
{
	double x;
	double y;
};	// defining a structure

typedef struct Point point;	// defining a new type using structure

point new_point(double c, double d)	// structure as return value
{
	point p;

	p.x = c;
	p.y = d;

	return p;
}

double distance(point a, point b)	// structure as parameter
{
	double d = 0.0;

	d = sqrt(pow(a.x - b.x, 2) + pow(a.y - b.y, 2));

	return d;
}

void modify_wrong(point p, double c, double d)
{
	p.x = c;	// modifying members inside function is temporary
	p.y = d;
}

void modify_pointer(point *p, double c, double d)
{
	p->x = c;	// modifying members using structure pointer is permanent
	p->y = d;	// -> notation 
}

int main()
{
	struct Point p, q;	// declaring using structure
	point s;	// declaring using type
	point t = {9.0, -5.0};	// initializing during declaration
	double d;
	point *ptr;

	printf("%lf %lf\n", p.x, p.y);	// by default, values are 0

	q.x = 4.0;	// accessing or modifying the members in a structure
	q.y = -3.0;	// . notation 

	d = distance(p, q);
	printf("Distance = %lf\n", d);

	//p = {9.0, -5.0};	// error
	//printf("%lf %lf\n", p.x, p.y);

	p = new_point(7.0, -1.0);
	printf("%lf %lf\n", p.x, p.y);

	modify_wrong(q, 7.0, -1.0);
	printf("%lf %lf\n", q.x, q.y);

	ptr = &p;
	modify_pointer(ptr, 2.0, -5.0);
	printf("%lf %lf\t%lf %lf\n", p.x, p.y, ptr->x, ptr->y);

	printf("Size of p is %d, size of ptr is %d\n", sizeof(p), sizeof(ptr));

	//if (q == p)	// error
	//	printf("Equal structures\n");
}