<?php
$weapons = ['fists', 'whip', 'gun', 'nuclear']; // don't change the order of weapon élément in the array
$opponentWeapon = rand(0,count($weapons)-1);

echo 'The weapon of the opponent is <b>' . $weapons[$opponentWeapon] . '</b><br/><br/>';

switch ($opponentWeapon) {
    case 0:
        // The gun beats the fists
        $indyWeapon = 2;
        break;
    case 1:
        // The fists beat the whip
        $indyWeapon = 0;
        break;
    case 2:
        // The whip beats the gun
        $indyWeapon = 1;
        break;
    default:
        $indyWeapon = -1;
    break;
}

if (-1 == $indyWeapon) // Yoga test -;)
    echo 'This case isn\'t considered';
else
    echo 'Indy choose <b>' . $weapons[$indyWeapon] . '</b> to fight with the opponent';