php calculcator

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<?php
 // Define to make this all one document
$page = $_GET['page'];

// Defining the "calc" class
class calc {
var $number1;
var $number2;

function add($number1,$number2)
{
$result =$number1 + $number2;
echo("The sum of $number1 and $number2 is $result<br><br>");
echo("$number1 + $number2 = $result");
exit;
}

function subtract($number1,$number2)
{
$result =$number1 - $number2;
echo("The difference of $number1 and $number2 is $result<br><br>");
echo("$number1 &#045 $number2 = $result");
exit;
}

function divide($number1,$number2)
{
$result =$number1 / $number2;

echo("$number1 divided by $number2 is $result<br><br>");
echo("$number1 ÷ $number2 = $result");
exit;
}

function multiply($number1,$number2)
{
$result =$number1 * $number2;
echo("The product of $number1 and $number2 is $result<br><br>");
echo("$number1 x $number2 = $result");
exit;
}
}
$calc = new calc();
?>
<TITLE>PHP Calculator v1</TITLE>
<form name="calc" action="?page=calc" method="POST">
Number 1: <input type=text name=value1><br>
Number 2: <input type=text name=value2><br>
Operation: <input type=radio name=oper value="add">Addition <input type=radio name=oper value="subtract">Subtraction <input type=radio name=oper value="divide">Division <input type=radio name=oper value="multiply">Multiplication</input><br>

<input type=submit value="Calculate">
</form>
<?php
if($page == "calc"){
$number1 = $_POST['value1'];
$number2 = $_POST['value2'];
$oper = $_POST['oper'];
if(!$number1){
echo("You must enter number 1!");
exit;
}
if(!$number2){
echo("You must enter number 2!");
exit;
}
if(!$oper){
echo("You must select an operation to do with the numbers!");
exit;
}
if(!eregi("[0-9]", $number1)){
echo("Number 1 MUST be numbers!");
exit;
}
if(!eregi("[0-9]", $number2)){
echo("Number 2 MUST be numbers!");
exit;
}
if($oper == "add"){
$calc->add($number1,$number2);
}
if($oper == "subtract"){
$calc->subtract($number1,$number2);
}
if($oper == "divide"){
$calc->divide($number1,$number2);
}
if($oper == "multiply"){
$calc->multiply($number1,$number2);
}
}
?>