Elseif Construct in PHP

The elseif construct allows you to specify conditions in the else block. Let's look at an example:

php<?php
  $num = 1;
  
  if ($num === 1) {
    echo 'variant 1';
  } elseif ($num === 2) {
    echo 'variant 2';
  } elseif ($num === 3) {
    echo 'variant 3';
  }
?>

The advantage of using elseif instead of multiple if statements is the ability to catch the situation when the value of the variable $num does not match any of the conditions:

php<?php
  $num = 1;
  
  if ($num === 1) {
    echo 'variant 1';
  } elseif ($num === 2) {
    echo 'variant 2';
  } elseif ($num === 3) {
    echo 'variant 3';
  } else {
    echo 'variant not supported';
  }
?>

Задание 1

The variable $day contains some number from the interval 1 to 31. Determine into which decade of the month this number falls (the first, second, or third).

Задание 2

Modify the previous task so that, if the variable $day contains not a number from 1 to 31, an error message is displayed.