Hulp nodig met switch (id)

4
Fatal error: Function name must be a string in C:\xampp\htdocs\optellen1.php on line 8

4
Fatal error: Function name must be a string in C:\xampp\htdocs\optellen1.php on line 8

<?PHP 
function optellen($getal1,$getal2) 
{ 
    $som = $getal1 + $getal2; 
    return $som;     
} 
echo optellen(1,3); 
switch ($optellen(1,8)) { 
   case 0: 
   case 1: 
   case 2: 
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
echo(" Het getal is lager als 10 ");
       
} 

?> 

<?PHP 
function optellen($getal1,$getal2) 
{ 
    $som = $getal1 + $getal2; 
    return $som;     
} 
echo optellen(1,3); 
switch ($optellen(1,8)) { 
   case 0: 
   case 1: 
   case 2: 
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
echo(" Het getal is lager als 10 ");
 
} 
 
?>

switch ($optellen(1,8)) { 
   case 0: 
   	echo "getal is 0";
	break;
	
   case 1: 
   	echo "getal is 1";
	break;
}

switch ($optellen(1,8)) { 
   case 0: 
   	echo "getal is 0";
	break;
 
   case 1: 
   	echo "getal is 1";
	break;
}