Day of the Year Program - php

Question

So I have this code that creates a drop down box to select a month, another drop down box to select the day, then a text field to type in a year. My question is what to do next in php to be able to select a certain month, day, and year to where, when i click "calculate," it will display what day of that year it is?
So for example, if i choose January 4 2015, when i click calculate, i want it to display 4 since it is the 4th day of the calendar year. How do I do that?
<form action="calc.php" method="post">
Month: <select name="month">
<option value="january">January</option>
<option value="february">February</option>
<option value="march">March</option>
<option value="april">April</option>
<option value="may">May</option>
<option value="june">June</option>
<option value="july">july</option>
<option value="august">August</option>
<option value="september">September</option>
<option value="october">October</option>
<option value="november">November</option>
<option value="december">December</option>
</select>
Day: <select name="day">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
<input name="entry" type="text" size="10" placeholder="Year">
<input type="submit" value="Calculate">
</form>

Answer 1

You can use date:
echo date("z", strtotime('2015-01-04'));
But it returns:
The day of the year (starting from 0)
So you need to add 1 to the result.

Answer 2

you can try the below code to get the day of the date . here i am using the same page for the post. if you are using another page for posting (i mean action page) use the php inside that file,
HTML
<form action="#" method="post">
Month: <select name="month">
<option value="01">January</option>
<option value="02">February</option>
<option value="03">March</option>
<option value="04">April</option>
<option value="05">May</option>
<option value="06">June</option>
<option value="07">july</option>
<option value="08">August</option>
<option value="09">September</option>
<option value="10">October</option>
<option value="11">November</option>
<option value="12">December</option>
</select>
Day: <select name="day">
<option value="01">1</option>
<option value="02">2</option>
<option value="03">3</option>
<option value="04">4</option>
<option value="05">5</option>
<option value="06">6</option>
<option value="07">7</option>
<option value="08">8</option>
<option value="09">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
<input name="year" type="text" size="10" placeholder="Year">
<input type="submit" name="submit" value="Calculate">
</form>
PHP
<?php
if(isset($_POST['submit']))
{
$date = $_POST['year'].'-'.$_POST['month'].'-'.$_POST['day'];
echo date("l", strtotime($date));
}
?>