if(display_message() = "The details have been sent successfully"){
    //do stuff
}

if(numer_of_users >= 150){
     //do stuff
}

if(typeof greeting == "undefined"){
     //do stuff
}

<?php
$paymentStatus = "3" ;

switch($paymentStatus) {
    case 1:
        echo "paid";
        break;
    
    case 2:
    case 3:
        echo "Payment Declined";
        break;

    
    case 0:
          echo "Pending Payment";
          break;

    default:
    echo "Unknwon Payment Status";


}

 function output($value = '') {
        echo '<pre>';
        print_r($value);
        echo '</pre>';
    }

output ($value);