EDIT: compiles but system is not centered

Makefile

@@ -7,22 +7,23 @@ LDFLAGS:=-lm -lSDL2
 #Path to the lib Vec2
 VPATH:=vec2 gfx planet
 
+HDR:=gfx/gfx.h planet/constants.h planet/planet.h vec2/vec2.h
 
 
 main: main.o vec2.o gfx.o planet.o
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
-run_tests: tests
+run_tests: vec2_tests
 	./$<
 
-tests: vec_tests.o vec2.o
+vec2_tests: vec_tests.o vec2.o
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
-planet.o: planet.h
+planet.o: ${HDR}
 
-vec2.o: vec2.h
+vec2.o: ${HDR}
 
-gfx.o: gfx.h
+gfx.o: ${HDR}
 
 clean:
 	rm -f *.o main tests

main.c

@@ -28,17 +28,17 @@ int main() {
 		gfx_present(ctxt);
 		gfx_clear(ctxt, COLOR_BLACK);
 		// begin : draw the current state of your system
-		show_system(ctxt, sys);
+		show_system(ctxt, &sys);
 		// end : draw state of system
 		// begin : update your system
-		update_system(sys, DELTA_T);
+		update_system(&sys, DELTA_T);
 		usleep(100000);
 		// end : update system
 		if (gfx_keypressed() == SDLK_ESCAPE) { break; }
 	}
 
 	// begin : Free your system
-	free_system(sys);
+	free_system(&sys);
 	// end : free system
 	gfx_destroy(ctxt);
 	return EXIT_SUCCESS;

planet/planet.c

@@ -3,6 +3,8 @@
 
 #include "constants.h"
 
+#define NB_PLANETS 4
+
 
 planet_t create_planet(double mass, vec2 pos) {
 	planet_t p;
@@ -18,23 +20,22 @@ system_t create_system(double delta_t) {
 	system.star = create_planet(M_SOLEIL, vec2_create_zero());
 	system.nb_planets = 4;
 	system.planets = malloc(system.nb_planets * sizeof(planet_t));
-	if (NULL == system.planets) return NULL;
-	double masses[system.nb_planets] = {
+	double masses[NB_PLANETS] = {
 			M_MERCURE,
 			M_VENUS,
 			M_TERRE,
 			M_MARS};
-	vec2 positions[system.nb_planets] = {
+	vec2 positions[NB_PLANETS] = {
 			vec2_create(PER_MERCURE, 0.0),
 			vec2_create(PER_VENUS, 0.0),
 			vec2_create(PER_TERRE, 0.0),
 			vec2_create(PER_MARS, 0.0)};
-	double eccentricities[system.nb_planets] = {
+	double eccentricities[NB_PLANETS] = {
 			E_MERCURE,
 			E_VENUS,
 			E_TERRE,
 			E_MARS};
-	double axis_major[system.nb_planets] = {
+	double axis_major[NB_PLANETS] = {
 			A_MERCURE,
 			A_VENUS,
 			A_TERRE,
@@ -47,21 +48,21 @@ system_t create_system(double delta_t) {
 		vel = sqrt(vel);
 		const vec2 ru = vec2_normalize(vec2_sub(system.planets[i].pos, system.star.pos));
 		const vec2 rp = vec2_create(-ru.y, ru.x);
-		const vec2 v = vec2_mul(vel, r);
+		const vec2 v = vec2_mul(vel, rp);
 		system.planets[i].prec_pos = vec2_sub(system.planets[i].pos, vec2_mul(delta_t, v));
 	}
 	return system;
 }
 
 
-void show_system(struct gfx_context_t* ctxt, system_t* system) {
+void show_system(struct gfx_context_t* ctxt, system_t* system, const uint32_t width, const uint32_t height) {
 	// draw sun
-	const coordinates xy_sun = vec2_to_coordinates_centered(vec2_normalize(system->star.pos));
+	const coordinates xy_sun = vec2_to_coordinates_centered(vec2_normalize(system->star.pos), width, height);
 	draw_full_circle(ctxt, xy_sun.column, xy_sun.row, 50, COLOR_YELLOW);
 	// draw planets
-	for (uint32_t i = 0; i < sys.nb_planets; ++i) {
+	for (uint32_t i = 0; i < system->nb_planets; ++i) {
 		const coordinates xy = vec2_to_coordinates_centered(
-				vec2_normalize(sys.planets[i].pos),
+				vec2_normalize(system->planets[i].pos),
 				ctxt->width,
 				ctxt->height);
 		draw_full_circle(ctxt, xy.column, xy.row, 20, COLOR_BLUE);
@@ -72,6 +73,7 @@ void show_system(struct gfx_context_t* ctxt, system_t* system) {
 void update_system(system_t* system, double delta_t) {
 	for (uint32_t i = 0; i < system->nb_planets; ++i) {
 		// apply the effects of the sun
+		const double r_star_2 = vec2_norm_sqr(vec2_sub(system->planets[i].pos, system->star.pos));
 		vec2 a = vec2_mul((G * system->star.mass) / r_star_2, vec2_normalize(system->planets[i].pos));
 		// apply the effects of all other planets
 		for (uint32_t k = 0; k < system->nb_planets; ++k) {

planet/planet.h

@@ -4,26 +4,29 @@
 #include "../vec2/vec2.h"
 #include "../gfx/gfx.h"
 
-typedef struct _planet
-{
+typedef struct _planet {
 	double mass;
 	vec2 pos;      // x(t)
 	vec2 prec_pos; // x(t - dt)
 } planet_t;
 
-typedef struct _system
-{
+typedef struct _system {
 	planet_t star;       // ex. The sun
 	uint32_t nb_planets; // The number of orbiting planets
-	planet_t *planets;   // An array of orbiting planets
+	planet_t* planets;   // An array of orbiting planets
 } system_t;
 
 // These functions are not mandatory to implement,
 // it's rather a hint of what you should have.
 planet_t create_planet(double mass, vec2 pos);
+
 system_t create_system(double delta_t);
-void show_system(struct gfx_context_t *ctxt, system_t *system);
-void update_system(system_t *system, double delta_t);
-void free_system(system_t *system);
+
+//void show_system(struct gfx_context_t *ctxt, system_t *system);
+void show_system(struct gfx_context_t* ctxt, system_t* system, const uint32_t width, const uint32_t height);
+
+void update_system(system_t* system, double delta_t);
+
+void free_system(system_t* system);
 
 #endif