Sending default parameter as null and use default value set in function

When you start the value parameters happens:

 function makecoffee($type = "cappuccino")
    {
        return "Making a cup of $type.\n";
    }
    echo makecoffee();
    echo makecoffee(null);
    echo makecoffee("espresso");
    ?>

The above example will output:

Making a cup of cappuccino.
Making a cup of .
Making a cup of espresso.

To fulfill what you want to check with conditions as follows:

function test($username, $is_active=1, $sent_email=1, $sent_sms=1) {

    if($sent_email!=1)
        $sent_email=1;
      echo $sent_email;  // It should print default ie 1

    }