Something

for($a=1;$a<100;$a++)
{ echo "1";
        if(!array_key_exists('subcat_'.$a.'_1_0', $_POST))
        { 
				break;
        }
       
        for($b=1;$b<100;$b++)
        { echo "3";
                if(!array_key_exists('subcat_'.$a.'_'.$b.'_0', $_POST))
                {  echo "4";
                        //$x = -1;
						break;
                }
       
                for($c=0;$c<100;$c++)
                {  echo "5";
                        if(!array_key_exists('subcat_'.$a.'_'.$b.'_'.$c, $_POST))
                        {    echo "6";
                               // $y = -1;
							   break;
                        }
                         
                                $categories[$a][$b][$c] = $_POST['subcat_'.$a.'_'.$b.'_'.$c];
							
                        
                }
        }
}