Do not understand how this array result happens

[Amalion]

I'm trying to learn to build a login sequence. In one part, I wanted to determine if the user left any of the 3 required fields blank: \[code\]foreach ( $_POST as $key => $value ) { if ( $key = "school_code" || $key = "user_name" || $key = "password" ) { if ( $value =http://stackoverflow.com/questions/2025756/="" ) { $a_blank[] = $key ; } } }if( @sizeof( $a_blank ) > 0 ) { echo '<pre>'; print_r( $a_blank ); echo '</pre>'; }\[/code\]If the user does not enter anything for school_code or user_name, but DOES enter a password and then clicks submit, the result is:\[code\]Array( [0] => 1 [1] => 1)\[/code\]Why isn't the array result like this (i.e., the values of $key)?\[code\]Array( [0] => school_code [1] => user_name)\[/code\]Thanks!