rectanglearea.php

<body background = "a.png">

<form action="rectanglearea.php" method="post">

<center>
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<h3>Please enter the Length and the Width of your rectangle.</h3>

Enter length: <input type="text" name="textL" placeholder= "Enter number"/> //textfield to enter the length, only integer is allowed, it will return to the text field when you type letter
<br>
<br>
Enter width: <input type="text" name="textW" placeholder= "Enter number"/> //same as length, it's to enter the width.
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<input type="submit" value="Submit" /> here is to submit the length and width
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</form>

<?php
if(isset($_POST['textL']) && isset($_POST['textW'])){  //to get the number you've been entered on the text field & also to specify on what will be calculated.
if(!empty($_POST['textL']) && !empty($_POST['textW'])){ //it's specify that when you entered nothing on the textfield the submit will not proceed to calculation.
if(!preg_match("([0-9])",$_POST['textL']) || !preg_match("([0-9])",$_POST['textW'])){
echo 'Enter only numbers.';
}
else{
$l = $_POST['textL'];
$w = $_POST['textW'];
echo "The rectangle with length $l and width $w has an area of ".calculate($l,$w); //the output of calculation.
}
}
}

function calculate($length, $width){
$area = $length * $width; //the calculation of the rectangle area.
return $area;
}
?>