In this tutorial you will learn how to build your own web based calendar using PHP. This calendar is made from two parts. On top there are the links to the previous and the next month, and below them is the calendar itself. It will show the selected month name with the year following and the days of the month bellow in a table view. You will need a good PHP editor to help you with your development or if you are experienced enough you can use a plain text editing software such as Notepad.

At the begining we have to decide how we are going to pass our parameters. We can use either 'hidden' input fields in out html code or pass them in the URL. In this tutorial we will use the second approach. We are going to need two parameters - one for the "month" and one for the "year". We will also need an array with month names:

<?php

$monthNames = Array("January", "February", "March", "April", "May", "June", "July", 

"August", "September", "October", "November", "December");

?>

First we need to check if we have set up our parameters already. If we have not, we set them to the current month and year. (For detailed explanation of date() function please refer to PHP Manual ).

<?php

if (!isset($_REQUEST["month"])) $_REQUEST["month"] = date("n");

if (!isset($_REQUEST["year"])) $_REQUEST["year"] = date("Y");

?>

Lets also set the variables that we are going to use in our calandar:

<?php

$cMonth = $_REQUEST["month"];

$cYear = $_REQUEST["year"];



$prev_year = $cYear;

$next_year = $cYear;

$prev_month = $cMonth-1;

$next_month = $cMonth+1;



if ($prev_month == 0 ) {

	$prev_month = 12;

	$prev_year = $cYear - 1;

}

if ($next_month == 13 ) {

	$next_month = 1;

	$next_year = $cYear + 1;

}

?>

$cMonth and $cYear are used for the current month and year displayed on the calendar. For the "Previous" and "Next" links we will need the coresponding parameters. We set $prev_year and $next_year to the current one. Later we may have to change this but for now it is OK. We also have to set parameters for the next and previous months by adding and subtracting 1. Now is the catch. We have to check if our parameter has not gone over or down the limit. Since there are 12 months in a year if our parameter goes to 13 then it means that another year has passed by and we have to set our "month" parameter back to 1 ( January ) and add 1 to our "year" parameter. The other way around is when we go back in time and our "month" parameter goes to 0. Then we have to decrease our "year" parameter by 1 and set the month paramether to 12 ( December ). Now as we set our links for previous and next months we turn to how to build the actual calendar.
We create a table that will hold our calendar and add the links in one row. Then we add a table in a new row that will hold the days. We also include the month name and the year in the first on the new table. But because arrays are zero based, we need to subtract one from the "month" parameter value to get the correct name.

<table width="200">

<tr align="center">

<td bgcolor="#999999" style="color:#FFFFFF">

<table width="100%" border="0" cellspacing="0" cellpadding="0">

<tr>

<td width="50%" align="left">  <a href="<?php echo $_SERVER["PHP_SELF"] . "?month=". $prev_month . "&year=" . $prev_year; ?>" style="color:#FFFFFF">Previous</a></td>

<td width="50%" align="right"><a href="<?php echo $_SERVER["PHP_SELF"] . "?month=". $next_month . "&year=" . $next_year; ?>" style="color:#FFFFFF">Next</a>  </td>

</tr>

</table>

</td>

</tr>

<tr>

<td align="center">

<table width="100%" border="0" cellpadding="2" cellspacing="2">

<tr align="center">

<td colspan="7" bgcolor="#999999" style="color:#FFFFFF"><strong><?php echo $monthNames[$cMonth-1].' '.$cYear; ?></strong></td>

</tr>

<tr>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>S</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>M</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>T</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>W</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>T</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>F</strong></td>

<td align="center" bgcolor="#999999" style="color:#FFFFFF"><strong>S</strong></td>

</tr>

Now we have to set the proper dates for our calendar. We have to make integer representation of the date so we can easily operate with it. Then we get the number of days of the selected month and the number representation (0 for Sunday through 6 for Saturday) of the first day of the month. All of these functions are fully explained in PHP Manual. Our loop that is going to print the dates starts at 0, because the days of the week start from 0 (Sunday). It has to loop through the number of days plus the offset of the first day of the month. We have to print new row for each week. We check this by modulus of the number of days in one week 7. If it equals 0 then it is the begining of the week and we print open row tag <tr> and if it is the end of the week 6 we print close tag for this week </tr>. All we need to do is to check if the day that we print is before $startday. In this case we print empty tag. Otherwise we have to print the date. We make it by subtracting the $startday. we have to add one because we don't want our dates to start from 0.

<?php 

$timestamp = mktime(0,0,0,$cMonth,1,$cYear);

$maxday = date("t",$timestamp);

$thismonth = getdate ($timestamp);

$startday = $thismonth['wday'];

for ($i=0; $i<($maxday+$startday); $i++) {

	if(($i % 7) == 0 ) echo "<tr>n";

	if($i < $startday) echo "<td></td>n";

	else echo "<td align='center' valign='middle' height='20px'>". ($i - $startday + 1) . "</td>n";

	if(($i % 7) == 6 ) echo "</tr>n";

}

?>

Now we add just the finishing touches of the html and we have finished the calendar.

</table>

</td>

</tr>

</table>