Nested if Statement good or bad?

I have a vote system that allows users to vote for items. Right now I am doing it by checking first if the user is logged in and then checking to see if they have already voted. I am wondering if there is a better way of doing this as I have been told that nested if statements are something to avoid.

My code:

if ($loggedIn) {
    if($row['voted']){
        You Already voted
    }else{
        <a href="#">Agree</a>
    }
}else{
    Please Register
}

Nested if( ... ){ ... }else{ ... } statements are fine, so long as they are logical and easy to read/maintain. Another option is to review the logic of your arguments and see if they can be expressed in a simpler fashion.

For example, your provided code could be expressed as:

if( !$loggedIn ){
  echo 'Please Register';
}elseif( $row['voted'] ){
  echo 'You Already voted';
}else{
  echo '<a href="#">Agree</a>';
}