Slot.php

<?php
// Our slot will be 3 reels, one win line, with 3 symbols.
// X, BAR and 7.
// 0 = X, 1 = BAR, 2 = 7

// This is the layout of the reels, running vertically. There are 20
// symbols on each reel.
$reels = [
   // reel 1 has 10 X's, 7 Bars and 3 7s
   [0,1,0,1,0,1,0,1,2,2,1,0,1,0,0,0,0,2,1,0],
   // reel 2 has 11 X's, 7 Bars and 2 7s
   [1,1,0,0,0,1,0,2,0,1,1,0,0,2,0,1,0,0,1,0],
   // reel 3 has 9 X's, 9 Bars and 2 7s
   [0,0,0,1,1,1,0,1,2,0,0,1,1,2,0,0,1,1,0,1],
];

// Let's map to the symbols:
$symbols = [
    0 => 'X',
    1 => 'B',
    2 => '7',
];

// Match 3 of the same symbol on the winline for a prize.
// Xs will be the lowest win at 2x, BARs will pay 10x, 7s will pay a whopping 100x
$paytable = [
    'X' => 2,
    'B' => 10,
    '7' => 100,
];

// How many spins our game will run for.
$spins = 100000;

// Bet size in £/$/whatever
$bet = 1;

// How much money have we spun through in bets?
$totalBet = 0;

// How much money have we won in total?
$totalWin = 0;

// What is the RTP over the number of spins, as a percentage?
$rtp = 0;

// Placeholder for counting the occurrences of each of the 3 possible types
// of win.
$wins = [
    'X' => 0,
    'B' => 0,
    '7' => 0,
];

// Game loop - run for $spins
for ($i=0; $i < $spins; $i++) {
    // Let's take the money!
    $totalBet = $totalBet + $bet;

    // We start by selecting a genuinely random reel position for each of the 3
    // reels. Remember - there are 20 possible positions on each reel.
    // The positions selected randomly are the symbols which will appear on
    // the win line.
    $reelPositions = [random_int(0, 19), random_int(0, 19), random_int(0, 19)];

    // What symbols do these positions map to? This creates the win line.
    $reelSymbols = [
        $symbols[$reels[0][$reelPositions[0]]], // first reel
        $symbols[$reels[1][$reelPositions[1]]], // second
        $symbols[$reels[2][$reelPositions[2]]], // third
    ];

    // At this point, $symbols contains something like ['X', 'X', 'B'] or
    // whatever our combination is. Let's display it in the form X-X-B.
    //echo implode('-', $reelSymbols)."\n";

    // Now let's calculate if it was a win. To be a win, it must be the same
    // symbol on all 3 reels.
    // One way we can do this is to count how many different symbols are
    // in the win line - if it's 1, they must all be the same.
    if (count(array_unique($reelSymbols)) === 1) {
        // It's a win. Let's compare the symbol on the win line to the paytable
        // and add that amount of money to the total wins.
        $totalWin = $totalWin + $paytable[$reelSymbols[0]];

        // Now let's add that symbol to our running count of how many wins
        // of each type took place.
        $wins[$reelSymbols[0]] = $wins[$reelSymbols[0]] + 1;
    }
}

// Let's calculate RTP. This is the total wins divided by the total bet, then
// multiplied by 100 to give a percentage.
$rtp = ($totalWin / $totalBet) * 100;

// Let's see what the results were:
echo 'Spins: '.$spins."\n";
echo 'Total bet: '.$totalBet."\n";
echo 'Total wins: '.$totalWin."\n";
echo 'Number of X-X-X: '.$wins['X']."\n";
echo 'Number of B-B-B: '.$wins['B']."\n";
echo 'Number of 7-7-7: '.$wins['7']."\n";
echo 'RTP: '.$rtp."\n";