function.php

<?php
function connectDB()
{
    $serverName = "127.0.0.1";
    $userName = "root";
    $userPassword = "";
    $dbName = "php_crud";

    $objCon = mysqli_connect($serverName, $userName, $userPassword, $dbName);
    mysqli_set_charset($objCon, "utf8");
    return $objCon;
}

function date_th($date)
{
    if ($date == '0000-00-00')
        return '-';

    $date_array = explode('-', $date);
    $th_date = $date_array[2] .
        '/' . $date_array[1] . '/' .
        ($date_array[0] + 543);

    return $th_date;
}

function date_en($date)
{
    $date_array = explode('/', $date);
    $en_date = ($date_array[2] - 543) . '-' .
        $date_array[1] . '-' . $date_array[0];
    return $en_date;
}

function randomString($length = 5)
{
    $str = "";
    $characters = array_merge(range('0', '9'));
    $max = count($characters) - 1;
    for ($i = 0; $i < $length; $i++) {
        $rand = mt_rand(0, $max);
        $str .= $characters[$rand];
    }
    return $str;
}