这个数字如何输出不了

这个数字怎么输出不了？

PHP code

<!--

Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/

-->$str = '12345678901234567890123456789012345678901234567890';

$num = $str + 1;

echo $num;

Copy after login

PHP code

$str = '12345678901234567890123456789012345678901234567890'; 
echo bcadd($str,'1'); <div class="clear">
                 
              
              
        
            </div>

Copy after login