/*
 * Contrived example of using "struct" to represent 2d point:
 * Define and demo/test some simple functions.
 */
#include <stdio.h>
#include <math.h>

/* point in 2d space */
typedef struct point2d {
	double x;
	double y;
} point2d_t;

/* function declarations -- descriptions with definitions below */
double distance(point2d_t p1, point2d_t p2);
double square(double d);
void scale(point2d_t *p, double factor);
void test_distance(point2d_t p1, point2d_t p2);
void test_scale(point2d_t p, double f);

/* main program */
int main(void) {
	point2d_t p1 = { 1.0, 1.0 };
	point2d_t p2 = { 4.0, 5.0 };
	point2d_t p3 = { 1.0, -1.0 };
	test_distance(p1, p2);
	test_distance(p1, p3);
	test_scale(p2, 2.0);
	test_scale(p2, -10.0);
	return 0;
}

/* convenience/"helper" function for distance() */
double square(double d) { return d*d; }

/* 
 * get distance between two points 
 */
double distance(point2d_t p1, point2d_t p2) {
	return sqrt(square(p1.x - p2.x) + square(p1.y - p2.y));
}

/* 
 * "scale" point -- multiply coordinates by scalar factor 
 * modifies p
 */
void scale(point2d_t *p, double factor) {
	(p->x) *= factor;
	(p->y) *= factor;
}

/* 
 * test/demo distance function -- call and print input/output nicely 
 */
void test_distance(point2d_t p1, point2d_t p2) {
	printf("distance between (%g, %g) and (%g, %g) is %g\n", 
			p1.x, p1.y, p2.x, p2.y, distance(p1, p2));
}

/* 
 * test/demo scale function -- call and print input/output nicely 
 */
void test_scale(point2d_t p, double f) {
	/* create a copy so we can print both "before" and "after" easily */
	point2d_t temp_p = p;
	scale(&temp_p, f);
	printf("(%g, %g) scaled by %g is (%g, %g)\n", 
			p.x, p.y, f, temp_p.x, temp_p.y);
}