help whats wrong with this code

[derksj]

if 
($a ='' && $b =='')
{
echo "no mail";
}
else
{
mail('[e-mail]',$subject,$messagepo,"$headers");
}
header("location:thanks.php");

why does this not work

[ahundiak]

$a = '' should be $a == ''

And make sure your variables are set.