if($skill = mining) {


 $levelup = $skilllevelnu+1;


 if($levelskill == $levelup)
  {
   echo "level up!";
  } 
} elseif($skill = crafting) {


 $levelup = $skilllevelnu+1;


 if($levelskill == $levelup)
  {
   echo "level up!";
  } 
}

<?php


$skills = array(
    'foo' => array(
        0, // begint bij 0
        83,
        174,
        276,
        388,
        512,
        ...,
    ),
    'bar' => array(
        0,
        1,
        11,
        21,
        1211,
        111221,
        312211,
        ...,
    ),
    ...,
);


// Skill foo
$foo_level = 1;
$foo_experience = 99;


// Skill bar
$bar_level = 5;
$bar_experience = 2000;


foreach($skills AS $skill => $milestones)
{
    rsort($milestones);


    foreach($milestones AS $level => $experience)
    {
        if ($level <= ${$skill.'_level'})
            break;


        if (${$skill.'_experience'} >= $experience)
        {
            $diff = $level - ${$skill.'_level'};
            echo 'Je bent '.$diff.' level'. ($diff > 1 ? 's' : '') .' omhoog gegaan in de skill '.$skill.'!';


            ${$skill.'_level'} = $level;
        }
    }
}