PHP calculator with words as operators - php

Question

I am stuck in resolving a PHP script.
I want to calculate a result from a set of instructions. Instructions comprise of a keyword and a number that are separated by a space per line. Instructions are loaded from file and results are output to the screen. Any number of Instructions can be specified. Instructions are operators (add, divide, subtract, multiply). The instructions will ignore mathematical precedence. The last instruction should be “apply” and a number (e.g., “apply 3”). The calculator is then initialised with that number and the previous instructions are applied to that number.
[Input]
add 2
multiply 3
apply 3
[Output]
15
[Explanation]
(3 + 2) * 3 = 15
example
[Input]
multiply 9
apply 5
[Output]
45
Can anyone help with some example logic or code ?
This is what I have tried so far:
class calculator {
public
function calculate($expression) {
$expression = str_replace(' ', '', $expression);
return $this - > exec($expression);
}
private
function exec($expression) {
switch ($expression['op']) {
case 'add':
$r = $expression[0] + $expression[1];
break;
case 'subtract':
$r = $expression[0] - $expression[1];
break;
case 'multiply':
$r = $expression[0] * $expression[1];
break;
case 'divide':
$r = $expression[0] / $expression[1];
break;
}
return $r;
}
private
function parseExpression($expression) {
$blankspace = preg_match('/\s/', $expression);
$counter = count($expression);
}
}

Answer 1

I would go this way:
class Calculator {
public $result = 0;
public $queue = Array();
public parseString($text) {
// parse input string
$cmds = explode(" ", $text);
foreach($cmds as $cmd) {
$cmd = trim($cmd);
if(!$cmd) continue; // blank or space, ignoring
$this->queue[] = $cmd;
}
// lets process commands
$command = false;
foreach($this->queue as $index => $cmd) {
if(is_number($cmd)) {
// if it's number fire previous command if exists
if(!$command || !method_exists($this, $command)) {
throw new Exception("Unknown command $command");
}
$this->$command($index, $cmd);
}else{
$command = $cmd;
}
}
}
public function apply($index, $number) {
// manipulate $result, $queue, $number
}
public function add($index, $number) {
// manipulate $result, $queue, $number
}
public function substract($index, $number) {
// manipulate $result, $queue, $number
}
}
$calculator = new Calculator();
$calculator->parseString('...');
It's just example how you can do it, but it's your job to do it :)
You gonna need to add some methods like clearQueue, clearResult, setResult etc...