How to provide default values for parameters

How to assign a default value to a parameter

A function with one default parameter

      function get_rand_bool_text($type = 'coin') { 

        $rand = random_int(0, 1); 

        switch ($type) { 

          case 'coin': 

              $result = ($rand == 1) ? 'heads' : 'tails';

              break; 

          case 'switch':

              $result = ($rand == 1) ? 'on' : 'off'; 

              break; 

          }

          return $result; 

      }

      get_rand_bool_text();

      echo("<p>get_rand_bool_text returns: ". get_rand_bool_text() . "</p>\n");
      get_rand_bool_text returns: tails

A function with an optional parameter

      function is_leap_year($date = NULL) { 

        if (!isset($date)) { 

          $date = new DateTime(); 

        } 

        if ($date->format('L') == '1') {

          return true; 

        } else {

          return false; 

        }

      }

      echo("<p>Leap year = " . is_leap_year() . "</p>\n");
      Leap year =

A function with one required and two default parameters

      function display_error($error, $tag = 'p', $class = 'error') { 

        $opentag = '<' . $tag . ' class="' . $class . '">'; 

        $closetag = ''; 

        echo $opentag . $error . $closetag; 

      }

      display_error("This is an error message!");
      This is an error message!

Calling a function with a default parameter value

Omitting optional parameters

      echo get_rand_bool_text(); // Displays 'heads' or 'tails' 

      echo display_error('Out of range'); // 'p' tag with 'error' class

      $is_leap_year = is_leap_year(); // true or false based on current date
      
      headsOut of range

Providing optional parameters

      echo get_rand_bool_text('switch'); // Displays 'on' or 'off'

      echo display_error('Out of range', 'li');

      Switch is off.
Out of range

To supply a default value for a parameter, code the parameter name followed by the equals sign and the default value. The default value must be a scalar value, an array of scalar values, or NULL. A scalar value is a literal number, string, or Boolean value. A scalar value cannot contain operators, variables, or function calls.
To code a function that sets a default value for a parameter, assign NULL to the param-eter. Then, within the function, you can check whether the parameter contains NULL. If so, you can write the code that sets the default value for the parameter.

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