PHP - how to display years,months and days based on two POST date?

Question

I am testing out whether I can get and display the duration that is between two dates based on post. These two dates are called from the database.

This is before I clicked the "Update Contract" .

This is after I clicked the "Update Contract" .

Php:

<?php
require("config.php");
$id = filter_input(INPUT_GET, 'id');
error_reporting( ~E_NOTICE );

if(isset($_POST['edit']) ){     
    $startdate = date('Y-m-d', strtotime($_POST['startdate']));
    $expdate = date('Y-m-d', strtotime($_POST['expdate']));
    $diff = abs(strtotime($expdate) - strtotime($startdate));

    $years = floor($diff / (365*60*60*24));
    $months = floor(($diff - $years * 365*60*60*24) / (30*60*60*24));
    $days = floor(($diff - $years * 365*60*60*24 - $months*30*60*60*24)/ (60*60*24));

    $upd= "UPDATE `contracts` SET  `startdate` = ?, `expdate` = ? WHERE `id` = ?";
    $stmt = $con->prepare($upd);
    $stmt->bind_param("ssi",$startdate,$expdate,$id);
    $stmt->execute();

        if ($stmt->errno){
        echo "FAILURE!!! " . $stmt->error;
        } else {
        $successMsg =  "Contract Successfully Updated!";
        }
        $stmt->close();     

    }

printf("%d years, %d months, %d days\n", $years, $months, $days);
?>

Form:

<form method="post" action="">
    <?php
    if(isset($successMsg)){
    ?>
    <div class="alert alert-success">
    <strong><?php echo $successMsg; ?></strong>

    <?php
    }
    ?>
    <?php

    $id = filter_input(INPUT_GET, 'id');
    $sql = "SELECT * FROM contracts WHERE `id` = $id";
    $result = $con->query($sql);
    $row = $result->fetch_assoc();  

    ?>
        <label>Start Date</label>
        <input type="date" name="startdate" value="<?php echo $row['startdate']; ?>"/>

        <label>Expiry Date</label>
        <input type="date" name="expdate" value="<?php echo $row['expdate']; ?>"/>                              

        <button type="submit" class="btn btn-success btn-md" name="edit">
        <span class="glyphicon glyphicon-pencil"></span> Update Contract
        </button>
</form>

The Problems are:

1. How can I display the duration without having to clicked on the "Update Contract" to see the updated duration?
2. The updated duration between the dates shown are not the exact duration as it is supposed to be 1 year, 11 months, 3 days.

Answer 1

Answer for second question:

make use of the native DateTime Class and it's related DateInterval :

<?php
$startdate=new DateTime($_POST['startdate']); 
$expdate=new DateTime($_POST['expdate']); 
$diff=$expdate->diff($startdate); 
print_r( $diff );
// or 
printf("%d years, %d months, %d days\n", $diff->y, $diff->m, $diff->d);

// for database input you'll have to format the dates like so:
echo $startdate->format('Y-m-d');

The solution to your first question is just about restructuring your code.
I suppose this is all in one php-file.

• check whether your form was posted, as you did.
• if so, do the database update
• if not, get the values from database - and set the same variable names ( $startdate = $row['startdate'] ;)
• in any case do the calculation, as above
• then display what you need (the difference, the form, a message...)