[PHP] Is this a bug?

[zhaoxd]

Hello all:
            
    Not long ago I wrote some php code in my computer which had a apache server,and my 
php version is 4.0.5.The code as followed:
    
    $num = 2886732778;
    settype($num, integer);
    echo $num;
    
    And I found the num is -2147483648.attention,please:the version of php is 4.0.5.
    
    When I installed php-4.2.0 in my computer,however,I found the output of result is 
-1408234499.

    Why did the difference between the two version php happen?Is this a bug???

Any help is appreciated!
                                                        zhaoxd