I really enjoyed the way you dealt damage to enemies; it reminded me of the Survivor.io Instagram advertisement, haha. It would be great to have information on the amount of damage I'm inflicting on the enemies and also display the enemy's life on the game screen – these are crucial elements to be shown.
Having a well-designed menu with settings would be a quick and straightforward addition. In the next game jam, you could simply adjust the theme and options for the menu if you wish.
By the way, for the damage aspect, you could check out my game to see how the damage popup appears when hitting a meteor; I think it would fit perfectly in this game.
Additionally, implementing a randomly generated map would add a lot of value to the overall experience.
Great job accomplishing all of this without an engine! I remember using SDL2 once for a Candy Crush game, and I initially struggled due to the lack of content explaining what I was trying to do, haha! :D