function IsEmail ($text) {
  	$text = strtolower($text);
  	/* for ($i=1; $i<=strlen($text); $i++)
  	{
    	if (strpos("abcdefghijklmnopqrstuvwxyz0123456789@.-_", substr($text, $i, 1)) === false)
    	{
			return false;
    	}
  	} */
	if (strlen($text) < 6)
	{
    	return false;
  	}
	if (strpos($text, "@") != strrpos($text, "@"))
	{
    	return false;
  	}
	if ((strpos($text, "@") < 1) || (strpos($text, "@") > (strlen($text) - 4)))
	{
    	return false;
  	}
	if (strrpos($text, ".") < strpos($text, "@"))
	{
    	return false;
  	}
	if (((strlen($text) - strrpos($text, ".") - 1) < 2) || ((strlen($text) - strrpos($text, ".") - 1) > 3))
	{
    	return false;
  	}
	return true;
} 

// převod znakové sady win-1250 na iso
function ToISO ($text) {
	$iso = "µľ®»«ą©Ą";
	$win = "ľžŽťŤšŠĽ";


	for ($i=1; $i<=strlen($win); $i++)
  	{
    	$text = str_replace(substr($win,$i-1,1), substr($iso,$i-1,1), $text);
  	}
  	return $text;
}

// náhrada funkce str_repeat
function StrRepeat ($text, $num) {
	for ($i=1; $i<=$num; $i++) { $temp = $temp . $text; }
	return $temp;
} 

// funkce mysql_query s výpisem případné chyby
function MySqlQuery ($query) {
	$sql_result = mysql_query($query);
	if (!$sql_result) {
		echo "<p><font face=\"Verdana, Arial, Helvetica, sans-serif\" size=\"2\"><font color=\"Red\"><b>MySQL Error</b></font> - ";
		echo mysql_errno().": ".mysql_error()."</font></p>";
	}
	return $sql_result;
} 

// převod do kódování MIME
function ToMIME ($text) {
	for ($i=1; $i<=strlen($text); $i++)
	{
    	if (ord(substr($text,$i-1,1)) == 61)
	    {
	    	$temp = $temp . "=3D";
		}
	    elseif (ord(substr($text,$i-1,1)) < 128)
	    {
			$temp = $temp . substr($text,$i-1,1);
	    }
		else
	    {
			$temp = $temp . "=" . substr(dechex(ord(substr($text,$i-1,1))), strlen(dechex(ord(substr($text,$i-1,1)))) - 2);
	    }
	} 
	return $temp;
}

// vrátí time +/- Den,Měsíc,Rok
function ConvertDate ($mounth, $day, $year) {
	$temp  = mktime (0,0,0,date("m")+$mounth  ,date("d")+$day,date("Y")+$year);
	return $temp;
}