<?php

if( isset( $_POST ['act' ])

&& ! empty( $_POST [ 'z1' ])

&& ! empty( $_POST [ 'z2' ])

&& is_numeric ( $_POST ['z1' ])

&& is_numeric ( $_POST ['z2' ]))

{

if ($_POST [ 'act' ] == 'add' )

{

$calc = ( $_POST [ 'z1' ]+ $_POST [ 'z2' ]);

$op = '+' ;

}

if ($_POST [ 'act' ] == 'sub' )

{

$calc = ( $_POST [ 'z1' ]- $_POST [ 'z2' ]);

$op = '-' ;

}

if ($_POST [ 'act' ] == 'div' )

{

$calc = ( $_POST [ 'z1' ]/ $_POST [ 'z2' ]);

$op = '/' ;

}

if ($_POST [ 'act' ] == 'mul' )

{

$calc = ( $_POST [ 'z1' ]* $_POST [ 'z2' ]);

$op = '*' ;

}

if ($_POST [ 'act' ] == 'pro' )

{

$calc = (( $_POST [ 'z2' ]* $_POST ['z1' ])/ 100 );

$op = '% of' ;

}

echo '

        <p>' . $_POST [ 'z1' ]. ' ' . $op .' ' . $_POST [ 'z2' ]. ' = ' . $calc . '</p>

        <p><a href="./">try again</a></p>' ;

} else{

echo '

        <form method="post" action="./">

                <input type="text" name="z1" size="5" />

                <select name="act">

                        <option value="add">[ + ]</option>

                        <option value="sub">[ - ]</option>

                        <option value="div">[ / ]</option>

                        <option value="mul">[ * ]</option>

                        <option value="pro">[ % ]</option>

                </select>

                <input type="text" name="z2" size="5" />

                <input type="submit" name="doit" value="calculate" />

        </form>' ;

}

?>