Is there any difference between "and" and "&&" operators in PHP?

I have the following code and don't think and is needed, i.e. && should be used, as there is nothing to assign the left part to?

if($_REQUEST['foo'] != 'abc' and $_REQUEST['bar'] == 'def')
{
    echo "all your base";
}

So it should be:

if($_REQUEST['foo'] != 'abc' && $_REQUEST['bar'] == 'def')
{
    echo "all your base";
}

Answer

In your case, && and and do the same thing, but take a look at the operator precedence. You can see that && and and are not on the same level, so mixing that could give you unexpected results in some cases - I recommend always using &&, but that's your choice.