diff --git a/du7/snake/snake.h b/du7/snake/snake.h
new file mode 100644
index 0000000..4d1ff74
--- /dev/null
+++ b/du7/snake/snake.h
@@ -0,0 +1,114 @@
+#ifndef snake_h_INCLUDED
+#define snake_h_INCLUDED
+
+// Number of food items on the plane
+#define FOOD_COUNT 5
+
+/**
+ * One part of the snake;
+ * 
+ * The snake is a linked list;
+ */
+ 
+struct snake {
+    // x position of the snake part
+    int x;
+    // y position of the snake part
+    int y;
+    // Pointer to the next snake part.
+    // The last part of the snake has NULL pointer to the next part.
+    struct snake* next;
+};
+
+// End game reason constants, return value of step_state
+enum endgame {
+    // Continue the game
+    END_CONTINUE = 0,
+    // Snake hit a wall
+    END_WALL,
+    // Snake hit itself
+    END_SNAKE,
+    // No food left
+    END_FOOD,
+    // Other reason to end
+    END_USER
+};
+
+/**
+ * State of the game.
+ * 
+ * The state consists of the snake, its speed and food on the plane.
+ * 
+ * The snake is a linked list of snake parts.
+ * 
+ * Speed vector is a vector added to the last head position to create a new head.
+ * 
+ * Food are points on the plane. Food with negative coordinates meads food is already eaten.
+ */
+ 
+struct state {
+    // Snake as a linked list
+    struct snake* snake;
+    // X of the food positions
+    int foodx[FOOD_COUNT];
+    // Y of the food positions
+    int foody[FOOD_COUNT];
+    int sx;
+    int sy;
+    int width;
+    int height;
+};
+
+/**
+ * Add a new snake part with given position. The new snake part becomes the new head.
+ *
+ * @param head of the snake.
+ * @param x coordinate of the new head;
+ * @param y coordinate of the new head.
+ * @return new head of the snake.
+ */
+struct snake* add_snake(struct snake* snake,int x,int y);
+
+/**
+ * Remove the last snake part.
+ * The last snake part  should always have NULL next pointer.
+ *
+ * @param head of the snake.
+ * @return new head of the snake.
+ */
+struct snake* remove_snake(struct snake* snake);
+
+/**
+ * Finds out if given coordinates are part of the snake.
+ * @param snake
+ * @param x coordinate to search in snake
+ * @param y coordinate to search in snake
+ * @return True, if there is a snake part with coordinates x,y. False otherwise
+ *
+ */
+int is_snake(struct snake* snake,int x, int y);
+/**
+ * Remove and free each snake part;
+ * @param head of the snake.
+ */
+void free_snake(struct snake* sn);
+/**
+ * Change game state.
+ *
+ * The function shoud calculate new posision of the snake head
+ * from the current position and speed vector.
+ * Then it should modify snake parst  or food coordinates according to the rules:
+ * 
+ * - If the new position is on the snake, end the game, return END_SNAKE.
+ * - If the new position is on the food, mark food as eaten
+ *   (set its coordinates to -1) and add new snake part on the position of the food. If there is no food left, return END_FOOD. else return END_CONTINUE.
+ * - If the new position is on the plane, add new snake part on the new position and remove the last part of the snake, return END_CONTINUE.
+ * 
+ * @param current state of the game
+ * @return reason to end the game according to enum endgame.
+ */
+int step_state(struct state* state);
+
+
+#endif // snake_h_INCLUDED
+