</p>
<ul>
<li>Only numbers and +,-,* and / operators are allowed in the expression.</li>
<li>The evaluation follows the standard operator precedence.</li>
<li>The calculator does not support parentheses.</li>
<li>The calculator handles invalid input "gracefully". It does not output PHP error messages.</li>
</ul>
<p>
<input type="text" name="expression">
<input type="submit" value="Calculate" name="submit">
</p>
<?php
if (isset($_POST['submit']) && isset($_POST['expression'])) {
check_expression($_POST['expression']);
}
function check_expression($expr)
{
/*GLOBAL VARIABLES*/
$invalid = false;
/*1. CHECK FOR INVALID CHARACTERS ERROR */
/*
allowed characters:
1.+
2.-
3.*
4./
5.0-9
*/
if (preg_match("/[^\\+\\-\\*\\/\\.0-9]/", trim($expr), $matches, PREG_OFFSET_CAPTURE)) {
function scan_extractive_expressions($variable)
{
if (!is_array($variable)) {
return;
}
if ($variable == array()) {
return;
}
if ($variable[0] == 'ARRAY_AT' || $variable[0] == 'CHAR_OF_STRING') {
check_expression($variable[1]);
}
if (($variable[0] == 'ARRAY_AT' || $variable[0] == 'DEREFERENCE') && count($variable[2]) != 0) {
scan_extractive_expressions($variable[2]);
}
}
