use of dropdown list PHP - php

Question

i have two questions. this is my code (Iranian calender), the problem is when i want see results. all values of year and month and day showns as '$year' and 'month' and 'day'.
<?php
echo'<select dir="rtl" name="year">';
for($year=1388;$year<=1410;$year++)
{
echo '<option value="$year">$year</option>';
}
echo'</select>';
echo'<select dir="rtl" name="month">';
for($month=1;$month<=12;$month++)
{
echo '<option value="$month">$month</option>';
}
echo'</select>';
echo'<select dir="rtl" name="day">';
for($day=1;$day<=31;$day++)
{
echo '<option value="$day">$day</option>';
}
echo'</select>';
?>
second question:
and i need another thing. in Iranian calendar month 1 to 6 have 31 days and 7 to 12 have 30 days so i need a conditional expression when user choose month 1 to 6 show 31 days to choose and when user chooses month 7 to 121 show 30 days.

Answer 1

You use double quotes inside of single quotes so it will be rendered as string.
Make the changes accordingly:
From:
echo '<option value="$year">$year</option>';
To:
echo '<option value="'.$year.'">'.$year.'</option>';
echo '<option value="'.$month.'">'.$month.'</option>';
echo '<option value="'.$day.'">'.$day.'</option>';
EDIT (answer to your second question):
JSFIDDLE
First you need to give an id attribute to your select fields.
<select dir="rtl" name="month" id="month">
<select dir="rtl" name="day" id="day">
Then you need to add some JQuery code that checks if month is greater than 6 so it will remove the last option (only if days are 31). If month is equal of 6 or less then will add a new option (only if days are 30).
$('#month').on('change', function() {
var monthValue = $(this).val();
var dayOptions = $('#day option').size();
if (monthValue > 6 && monthValue <=12) {
if (dayOptions == 31) {
$("#day option:last").remove();
}
} else if (monthValue >= 1 && monthValue <= 6) {
if (dayOptions == 30) {
$('#day').append($('<option>', {
value: 31,
text: 31
}));
}
}
});

Answer 2

you need to use " or use concatenation with . with '
so this should be:
echo '<option value="$day">$day</option>';
this:
echo '<option value="' . $day . '">' . $day . '</option>';
or this:
echo "<option value=\"$day\">$day</option>";