Fatal error: Cannot pass parameter by reference in PHP

Fatal error: Cannot pass parameter  by reference in PHP.

$stmt->bind_param("ssss",$userid,$theme,$title,"test");

The error is with 'test' in the bind_param call.

All parameters to bind_param must be passed by reference. A string is a primitive value, and cannot be passed by reference.

You can fix this by creating a variable and passing that as a parameter instead:

$testvar="test";

$stmt->bind_param("ssss",$userid,$theme,$title,$testvar);