# How do I change the turn from a user to the next?

I was asked by a friend to develop a small web game which should support 10 players. Very basic game-play: There is a piñata which has x-"healthpoints". Each player can hit the piñata when it's their turn.

However, I'm having a hard time figuring out how to handle this. As of now, I have three databases:

Table: game

• hasStarted
• usersTurn

Table: users

• id

TABLE: usersPlaying

• id

So far my game works like this:

'users' holds all of the users.

When the game starts all of the online users username are copied into 'usersPlaying'. Then a random row from 'usersPlaying' is selected and that username is copied into 'game' in the 'usersTurn' field.

From the webpage there's a AJAX-script checking for 'usersTurn' variable every second. If the username matches $_SESSION["username"] the users will know if it's their turn. However from here, I've totally lost it. I cannot figure out how to move on to the next player, and I'm even wondering if this is the right way to go at all. It's not ment to be too fancy, it's only going to be used once or twice. So with my hands folded - is there anyone who can point me in the right direction? • Is there some backend over which the users are connected or are they just reading/ writing each to the database directly? If you do have a backend, just add all playing users in a list and after each interaction, increase the index. When you are at the end, reset the index to 0. Can be as well used to check if the current user interaction is the active player Feb 22, 2021 at 19:17 ## 1 Answer Whenever you're dealing with a game where multiple players on their own machine are playing the same game (i.e. the same game "session", if you will), the easiest approach is always to play the game on the server (i.e. the backend), and have the players' machine (i.e. the webpage they are on, the frontend) merely represent the state of the game on the server and decide the UI based on the server game's state. Your situation is perfect for this approach. Now I can't (and won't) write the whole thing for you, but I'll help you get started on the basics. I strongly suggest adding an turnOrder field to usersPlaying, to keep track of whose turn it is next. If you're using a database, you're not always guaranteed to get the data with the same order, unless you specifically tell the database to order the data. I would suggest rename userPlaying in game to currentTurnOrder. Assuming a player set like this: UserId GameId TurnOrder Andy 1 1 Bob 1 2 Chris 1 3 You can calculate the next turn, and whose turn it is, using the following formula: $game.CurrentTurnOrder = (($game.CurrentTurnOrder + 1) %$number_of_players) + 1;


To walk you through the formula:

• ($game.CurrentTurnOrder + 1) increases the turn counter • %$number_of_players ensures that when the turn counter goes beyond the amount of players, it loops back to the beginning
• The final + 1 is added because % returns a 0-indexed value, but we've made turnOrder a 1-indexed value, so + 1 to fix it. If you store your turnOrder as a 0-indexed value, you don't need to do this step.

If you run this method several times, you will see that $nextTurnOrder changes value to 1,2,3,1,2,3,1,2,3,... and therefore creating a perfect match with each player's turnOrder column. For the sake of example, if you had a list of 5 players, , you will see that $nextTurnOrder changes value to 1,2,3,4,5,1,2,3,4,5,1,2,..., so you can see that the same formula neatly cycles over all players for any arbitrary amount of players.

So, in order for a given webpage to check if it's their turn, you check the game's current turn order, and see if it matches the local player's TurnOrder value.

The basic approach on the webpage is as follows:

• Load the initial game data, including this player's TurnOrder
• Keep checking the game's CurrentTurnOrder value
• When the game's CurrentTurnOrder matches this player's TurnOrder, it is this player's turn.