diff --git a/Makefile b/Makefile
index af9a5b3..0c12939 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ GTK_CFLAGS=$(shell pkg-config --cflags $(GTK_PACKAGES))
 GTK_LIBS=$(shell pkg-config --libs $(GTK_PACKAGES))
 
 # PROFILING_CFLAGS=-pg
-CFLAGS=-Wall -g -O2 $(PROFILING_CFLAGS) $(GTK_CFLAGS)
+CXXFLAGS=-Wall -g -O2 $(PROFILING_CFLAGS) $(GTK_CFLAGS)
 
 LIBS=$(GTK_LIBS) -lm
 
@@ -14,13 +14,13 @@ PROGS=balls
 OBJS=balls.o c_index.o game.o gravity.o spaceship.o main.o
 
 # dependencies (gcc -MM *.c)
-balls.o: balls.c game.h balls.h gravity.h
-c_index.o: c_index.c balls.h game.h c_index.h
-game.o: game.c game.h
-gravity.o: gravity.c gravity.h game.h
-main.o: main.c game.h balls.h c_index.h gravity.h spaceship.h
-spaceship.o: spaceship.c balls.h game.h
-stats.o: stats.c
+balls.o: balls.cc game.h balls.h gravity.h
+c_index.o: c_index.cc balls.h game.h c_index.h
+game.o: game.cc game.h
+gravity.o: gravity.cc gravity.h game.h
+main.o: main.cc game.h balls.h c_index.h gravity.h spaceship.h
+spaceship.o: spaceship.cc balls.h game.h
+stats.o: stats.cc
 
 .PHONY: run
 run: balls
diff --git a/balls.c b/balls.cc
similarity index 91%
rename from balls.c
rename to balls.cc
index 4d75d45..fc9d25b 100644
--- a/balls.c
+++ b/balls.cc
@@ -28,9 +28,9 @@ static void random_velocity(struct ball * p) {
 }
 
 void balls_init_state () {
-    static const unsigned int border = 10;
-    unsigned int w = width < 2*border ? 1 : width - 2*border;
-    unsigned int h = height < 2*border ? 1 : height - 2*border;
+    static const int border = 10;
+    int w = width < 2*border ? 1 : width - 2*border;
+    int h = height < 2*border ? 1 : height - 2*border;
 
     for (unsigned int i = 0; i < n_balls; ++i) {
 	balls[i].x = border + rand() % w;
@@ -141,7 +141,7 @@ static double random_color_component() {
 };
 
 static struct ball_face * new_ball_face(unsigned int radius, cairo_surface_t * face, int rotation) {
-    struct ball_face * f = malloc(sizeof(struct ball_face));
+    struct ball_face * f = (struct ball_face *)malloc(sizeof(struct ball_face));
     if (!f)
 	return 0;
     if (face && rotation) {
@@ -149,12 +149,12 @@ static struct ball_face * new_ball_face(unsigned int radius, cairo_surface_t * f
     } else {
 	f->rotations = 1;
     }
-    f->c_faces = malloc(sizeof(cairo_surface_t *)*f->rotations);
+    f->c_faces = (cairo_surface_t **)malloc(sizeof(cairo_surface_t *)*f->rotations);
     if (!f->c_faces) {
 	free(f);
 	return 0;
     }
-    for (int i = 0; i < f->rotations; ++i) {
+    for (unsigned int i = 0; i < f->rotations; ++i) {
 	f->c_faces[i] = gdk_window_create_similar_surface(gtk_widget_get_window(canvas),
 							  CAIRO_CONTENT_COLOR_ALPHA,
 							  2*radius, 2*radius);
@@ -204,7 +204,7 @@ static void balls_init_faces () {
     }
     if (face_surface) {
 	faces_count = radius_max + 1 - radius_min;
-	faces = malloc(sizeof(struct ball_face *)*faces_count);
+	faces = (struct ball_face **)malloc(sizeof(struct ball_face *)*faces_count);
 	for (unsigned int i = 0; i < faces_count; ++i)
 	    faces[i] = 0;
 	for(struct ball * b = balls; b != balls + n_balls; ++b) {
@@ -216,7 +216,7 @@ static void balls_init_faces () {
 	cairo_surface_destroy (face_surface);
     } else {
 	faces_count = n_balls;
-	faces = malloc(sizeof(struct ball_face *)*faces_count);
+	faces = (struct ball_face **)malloc(sizeof(struct ball_face *)*faces_count);
 	for (unsigned int i = 0; i < n_balls; ++i)
 	    balls[i].face = faces[i] = new_ball_face(balls[i].radius, 0, face_rotation);
     }
@@ -244,7 +244,7 @@ void balls_draw (cairo_t * cr) {
 static void balls_destroy_faces () {
     if (!faces)
 	return;
-    for (int i = 0; i < faces_count; ++i) {
+    for (unsigned int i = 0; i < faces_count; ++i) {
 	if (faces[i]) {
 	    if (faces[i]->c_faces) {
 		for (unsigned int j = 0; j < faces[i]->rotations; ++j)
@@ -265,7 +265,7 @@ void balls_destroy () {
 }
 
 void balls_init () {
-    balls = malloc(sizeof(struct ball)*n_balls);
+    balls = (struct ball *)malloc(sizeof(struct ball)*n_balls);
     assert(balls);
     balls_init_state ();
     balls_init_faces ();
diff --git a/c_index.c b/c_index.cc
similarity index 94%
rename from c_index.c
rename to c_index.cc
index 61ee3f5..44678e5 100644
--- a/c_index.c
+++ b/c_index.cc
@@ -96,7 +96,7 @@ static void c_index_insert(struct bt_node * t, struct bt_node * n, struct ball *
 
 void c_index_build() {
     c_index_init_node(c_index, balls);
-    for(int i = 1; i < n_balls; ++i)
+    for(unsigned int i = 1; i < n_balls; ++i)
 	c_index_insert(c_index, c_index + i, balls + i);
 }
 
@@ -150,11 +150,11 @@ void c_index_check_collisions(void (*collision)(struct ball *, struct ball *)) {
 
 int c_index_init() {
     if (!c_index)
-	c_index = malloc(sizeof(struct bt_node) * n_balls);
+	c_index = (struct bt_node *) malloc(sizeof(struct bt_node) * n_balls);
     if (!c_index)
 	return 0;
     if (!c_index_stack)
-	c_index_stack = malloc(sizeof(struct bt_node *) * n_balls);
+	c_index_stack = (struct bt_node **) malloc(sizeof(struct bt_node *) * n_balls);
     if (!c_index_stack)
 	return 0;
     return 1;
diff --git a/game.c b/game.cc
similarity index 77%
rename from game.c
rename to game.cc
index ab4a9f0..bb8b694 100644
--- a/game.c
+++ b/game.cc
@@ -11,8 +11,8 @@
 
 double delta = DEFAULT_DELTA;	/* seconds */
 
-unsigned int width = DEFAULT_WIDTH;
-unsigned int height = DEFAULT_HEIGHT;
+int width = DEFAULT_WIDTH;
+int height = DEFAULT_HEIGHT;
 
 /* Graphics System
  */
diff --git a/game.h b/game.h
index cba025d..f34c5ab 100644
--- a/game.h
+++ b/game.h
@@ -10,8 +10,8 @@ extern double delta;		/* simulation time delta in seconds */
 
 #define DEFAULT_DELTA 0.01
 
-extern unsigned int width;	/* game canvas width */
-extern unsigned int height;	/* game canvas height */
+extern int width;	/* game canvas width */
+extern int height;	/* game canvas height */
 
 #define DEFAULT_WIDTH 800
 #define DEFAULT_HEIGHT 800
diff --git a/gravity.c b/gravity.cc
similarity index 100%
rename from gravity.c
rename to gravity.cc
diff --git a/main.c b/main.cc
similarity index 97%
rename from main.c
rename to main.cc
index 37a1c12..e9108f5 100644
--- a/main.c
+++ b/main.cc
@@ -19,10 +19,10 @@
 /* Trivial collision check
  */
 void check_collisions_simple () {
-    for(int i = 0; i < n_balls; ++i)
-	for(int j = i + 1; j < n_balls; ++j)
+    for(unsigned int i = 0; i < n_balls; ++i)
+	for(unsigned int j = i + 1; j < n_balls; ++j)
 	    ball_elastic_collision(balls + i, balls + j);
-    for(int j = 0; j < n_balls; ++j)
+    for(unsigned int j = 0; j < n_balls; ++j)
 	ball_elastic_collision(&spaceship, balls + j);
    gravity_collisions (balls, balls + n_balls);
    gravity_collisions (&spaceship, &spaceship + 1);
@@ -31,7 +31,7 @@ void check_collisions_simple () {
 void check_collisions_with_index () {
     c_index_build();
     c_index_check_collisions(ball_elastic_collision);
-   for(int j = 0; j < n_balls; ++j)
+   for(unsigned int j = 0; j < n_balls; ++j)
 	ball_elastic_collision(&spaceship, balls + j);
    gravity_collisions (balls, balls + n_balls);
    gravity_collisions (&spaceship, &spaceship + 1);
@@ -42,7 +42,7 @@ void (*check_collisions)() = 0;
 void update_state () {
     if (check_collisions)
 	check_collisions();
-    for(int i = 0; i < n_balls; ++i)
+    for(unsigned int i = 0; i < n_balls; ++i)
 	ball_update_state(balls + i);
     spaceship_update_state();
 }
diff --git a/spaceship.c b/spaceship.cc
similarity index 100%
rename from spaceship.c
rename to spaceship.cc
diff --git a/stats.c b/stats.cc
similarity index 100%
rename from stats.c
rename to stats.cc