<?php
declare(strict_types=1);
$users = [
    'names' => [
        'janusz',
        'admin'
    ],
    'wallets' => [
        500,
        200
    ],
    'passwords' => [
        'haslo',//haslo janusza
        'admin'//haslo admina
    ]
];

$login = 'somsiad';
$password = 'haslo';
helloUser($login, $password);

function helloUser(string $login, string $password)
{
    global $users;
    $userId = array_search($login, $users['names'], true);
    if (in_array(strtolower($login), $users['names'], true) and $password === $users['passwords'][$userId]) {
        echo 'Witaj ' . $login . ', w twoim portfelu jest ' . $users['wallets'][$userId] . ' zł!';
    } else {
        echo 'Zły login lub hasło';
    }
}