so um how do you add a combat system in a text adventure game

Something similar to turn-based RPG combat.Just a loop where you choose options until the enemy has died or when player has died.

whats the line(s) of code

It depends on how complicated you want it to be. Since your game is text-based, i think is better just to post a hardcoded result instead of relying on the player's choiced in-battle. Something like: "You fighted that ugly spider, and you won!" But if you want it to be variable, then this algorithm can help you:

1.- Select a choice to attack (Punch or Kick for example). 2.- Substract the enemy life for the damage received. 3.- Enemy attack you. 4.- Substract your life by the damage received. 5.- Go to first step. And so on.

Also, no code here because understanding your tools and the logic is part of the task. Every App/Game is a task with unique challenges, so is up to you to find a solution for those problems instead of relying on copy-paste.