Problem with program in PHP [duplicate]

I'm needing help with an exercise in php that I'm doing. I'm getting the following error message:

  

Notice: Undefined offset: 1 in C: \ xampp \ htdocs \ calendario.php on line 5

You receive the same error message for lines 5 through 10 of the code. These lines refer to the screen printing of the values that should be in a vector. From the error message, it looks like the vector did not receive the correct values.

The following code is integrated:

<?php 
    function linha($semana){
        echo "<tr>
                <td>{$semana[0]}</td>
                <td>{$semana[1]}</td>
                <td>{$semana[2]}</td>
                <td>{$semana[3]}</td>
                <td>{$semana[4]}</td>
                <td>{$semana[5]}</td>
                <td>{$semana[6]}</td>           
             </tr>";
    }

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

?>

<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>