diff --git a/du4/snake.c b/du4/snake.c
new file mode 100644
index 0000000..4d6cac1
--- /dev/null
+++ b/du4/snake.c
@@ -0,0 +1,72 @@
+#include "snake.h"
+#include <stdlib.h>
+
+struct snake* add_snake(struct snake* snake, int x, int y) {
+    struct snake* nova_hlava = malloc(sizeof(struct snake));
+    nova_hlava->x = x;
+    nova_hlava->y = y;
+    nova_hlava->next = snake;
+    return nova_hlava;
+}
+
+struct snake* remove_snake(struct snake* snake) {
+    if (snake == NULL) return NULL;
+    if (snake->next == NULL) {
+        free(snake);
+        return NULL;
+    }
+    struct snake* aktualny = snake;
+    while (aktualny->next->next != NULL) {
+        aktualny = aktualny->next;
+    }
+    free(aktualny->next);
+    aktualny->next = NULL;
+    return snake;
+}
+
+void free_snake(struct snake* sn) {
+    while (sn != NULL) {
+        struct snake* dalsi = sn->next;
+        free(sn);
+        sn = dalsi;
+    }
+}
+
+int is_snake(struct snake* snake, int x, int y) {
+    struct snake* aktualny = snake;
+    while (aktualny != NULL) {
+        if (aktualny->x == x && aktualny->y == y) return 1;
+        aktualny = aktualny->next;
+    }
+    return 0;
+}
+
+int step_state(struct state* st) {
+    int nx = (st->snake->x + st->sx);
+    int ny = (st->snake->y + st->sy);
+
+    if (nx < 0 || nx >= st->width ||
+        ny < 0 || ny >= st->height) {
+        return END_WALL;
+    }
+
+    if (is_snake(st->snake, nx, ny)) {
+        return END_SNAKE;
+    }
+
+    for (int i = 0; i < FOOD_COUNT; i++) {
+        if (st->foodx[i] == nx && st->foody[i] == ny) {
+            st->snake = add_snake(st->snake, nx, ny);
+            st->foodx[i] = -1;
+            st->foody[i] = -1;
+            for (int j = 0; j < FOOD_COUNT; j++) {
+                if (st->foodx[j] >= 0) return END_CONTINUE;
+            }
+            return END_FOOD;
+        }
+    }
+
+    st->snake = add_snake(st->snake, nx, ny);
+    st->snake = remove_snake(st->snake);
+    return END_CONTINUE;
+}