calc.php

<?php
// Work out result of sum, without using eval or regular expressions
// Code should parse/tokenize the input string, and return the result.
// Simple functions such as str_replace(), strpos(), substr() can be used
// NO external libraries may be used

/**
 * Return answer, operator precedence ( / * - + ) must be retained.
 * @param String $sum Input
 * @return String The result of the sum
 */
function calc($sum) {

}

header('Content-type:text/plain');

// Should print 100
print calc("10*10")."\n";
// Should print 19
print calc("20+-1")."\n";
// Should print 3
print calc("3*3/3")."\n";
// Should print -1180
print calc("-100*23/2+-30")."\n";