十进制转二进制

function dec2bin ($dec) {
    $flag = array();
    while ($dec != 0) {
         array_push($flag,$dec%2);
         $dec = (int)($dec/2);
    }
    $binstr = '';
    while (!empty($flag)) {
        $binstr .= array_pop($flag);
    }
    return $binstr;
}
echo dec2bin(7);

注意：以上只是为了练习。PHP已经有内嵌函数decbin()以及base_convert(); 

echo &#39;<br/>&#39;;
echo base_convert(7,10,2);
echo &#39;<br/>&#39;;
echo base_convert(1111,2,8);
echo &#39;<br/>&#39;;
echo decbin(6);