年龄计算器不显示计算出的年龄

Question

This code is for computation of age based on the Selected Value of the user using the combo box and it must display the age in the text box provided below. The age must refreshed every time the user changes selected value in the combo box. but my current code does not the computed age does not show.

<?php
                $month = date("m"); //without leading zero(o)
                $year = date("Y"); //four digit format
                $day = date("d");
                $st_year = "1950"; //Starting Year
                $month_names = array("January", "February", "March","April", "May", "June", "July", "August", "September", "October", "November", "December");
            ?>

            <form name="Month_Year" id="Month_Year"  method="post">
            <select name="month" id="month">
            <?php
            for ($i=1; $i<=12; $i++) {
                echo "<option ";
                if ($i == $month) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">", $month_names[$i-1], "</option>\n";
            }
            ?>
            </select>
            <select name="year" id="year">
            <?php
            for ($i=$st_year; $i<=$year; $i++) {
                echo "<option ";
                if ($i == $year) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">$i</option>\n";
            }
            ?>
            </select>
            <select name="day" id="day">
            <?php
            for ($i=1; $i<=31; $i++) {
                echo "<option> ";
                if ($i == $day) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">$i</option>\n";
            }
            ?>
            </select>
            // I used this code to combine the selected value in the combo box.
            <?php $Convertdays = $month."/".$day."/".$year; 

            echo $Convertdays;
            ?>
            <script type="text/javascript">
            var birth = new Date( <?php '$Convertdays'?>);
            var check = new Date();
            var milliDay = 1000 * 60 * 60 * 24; // a day in milliseconds;
            var ageInDays = (check - birth) / milliDay;
            var ageInYears =  Math.floor(ageInDays / 365 );
            var age =  ageInDays / 365 ;
            </script>

Every time I change the value of the combo box, the textbox displays 0. Lets assume that the values of the Textboxes are October 19 1991 it should display 21

Answer 1

Move the javascript up top and make it a function so you can reference it

Then add the onChange() to trigger the function when you change your select elements

finally have the function output your calculation to somewhere on the page

<?php
    $month = date("m"); //without leading zero(o)
    $year = date("Y"); //four digit format
    $day = date("d");
    $st_year = "1950"; //Starting Year
    $month_names = array("January", "February", "March","April", "May", "June", "July", "August", "September", "October", "November", "December");
    $Convertdays = $month."/".$day."/".$year; 
?>
<script type="text/javascript">
    function update() {
        var e = document.getElementById("month");
        var month = e.options[e.selectedIndex].value;
        e = document.getElementById("day");
        var day = e.options[e.selectedIndex].value;
        e = document.getElementById("year");
        var year = e.options[e.selectedIndex].value;
        var birthDate = month + "/" + day + "/" + year
        var birth = new Date(year,month,day,0,0,0);
        var check = new Date();
        var milliDay = 1000 * 60 * 60 * 24; // a day in milliseconds;
        var ageInDays = (check - birth) / milliDay;
        var ageInYears =  Math.floor(ageInDays / 365 );
        var age = parseInt(ageInDays / 365) ;
        if (age < 3) {
            document.getElementById('Calculated').innerHTML = "You are under 3 years old, why are you on the computer?";
        } else {
            document.getElementById('Calculated').innerHTML = "You are " + age;
        }
    }
</script>
Enter your birth Date:
<div style="height:15px;"></div>
<form name="Month_Year" id="Month_Year"  method="post">
    <select name="month" id="month" style="margin-right: 30px;" onChange="update();">
        <?php
            for ($i=1; $i<=12; $i++) {
                echo "<option ";
                if ($i == $month) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">", $month_names[$i-1], "</option>\n";
            }
        ?>
    </select>
    <select name="day" id="day" style="margin-right: 30px;" onChange="update();">
        <?php
            for ($i=1; $i<=31; $i++) {
                echo "<option ";
                if ($i == $day) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">$i</option>\n";
            }
        ?>
    </select>
    <select name="year" id="year" onChange="update();">
        <?php
            for ($i=$st_year; $i<=$year; $i++) {
                echo "<option ";
                if ($i == $year) {
                    echo "selected=\"selected\" ";
                }
                echo "value=\"$i\">$i</option>\n";
            }
        ?>
    </select>
    <br>
</form>
<div id="Calculated">
    calculated age goes here<br>
</div>