desafios.php

<?php

function hora_do_dia() {
  $hora = date('H:i:s');
  if ($hora < '12:00:00') {
    echo "Bom dia!";
  }
  if ($hora >= "12:00:00" && $hora < "18:00:00") {
    echo "Boa tarde!";
  }
  if ($hora >= "18:00:00") {
    echo "Boa noite!";
  }
}

hora_do_dia();
echo  "<br/>";
echo  "<br/>";
//--------------------------------------------

function linha($semana)
{
  echo "<tr>";
  for ($i = 0; $i <= 6; $i++) {
    if (isset($semana[$i])) {
      if ($semana[$i] == date('d')) {
        echo "<td><strong>{$semana[$i]}</strong></td>";
      } else {
        echo "<td>{$semana[$i]}</td>";
      }
    } else {
      echo "<td></td>"; 
    } 
  }
  echo "</tr>";
}

function calendario()
{
  $dia = 1;
  $semana = array();
  while ($dia <= 31) {
    array_push($semana, $dia);
    if (count($semana) == 7) {
      linha($semana);
      $semana = array();
    }
    $dia++;
  }
  linha($semana);
}
?>

<table border="1">
  <tr>
    <th>Dom</th>
    <th>Seg</th>
    <th>Ter</th>
    <th>Qua</th>
    <th>Qui</th>
    <th>Sex</th>
    <th>Sáb</th>
  </tr>
  <?php calendario(); ?>
</table>