php calculator class

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

this is what i have tried but i cant get the logic to complete the methods

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('...');

how can i call or switch the add,divide,multiply,substract and how to distinguish and trigger apply word

any kind of help will be appreciated.

Answer 1

Try using the array_shift and array_pop functions:

//pop the apply num off end off the queue
$result= array_pop($this->queue); 
//now pop the apply operator off end of the queue
$operator = array_pop($this->queue); 

//now get the first operator and numbers using array_shift
$operator = array_shift($this->queue); //get first operator
$num = array_shift($this->queue); //get first number

//loop perform operation on result using number till done.
while($num !== null)
{
  $result = $operator($result, $num);
  $operator = array_shift($this->queue);
  $num = array_shift($this->queue);
}

Answer 2

You should process the apply first and then cut it out of your queue array. Before you start looping through with the commands, simply test for the apply command and run it first. This simplifies the whole process.

After many minutes of experimentation and chatting, has been resolved.

<?php
error_reporting(E_ALL);
class Calculator {

public $result = 0;
public $queue = array();

public function parseString($text) {

    // parse input string
    $split = explode(" ", $text); //This gets your input into new lines
    for ($i = 0; $i < count($split); $i += 2) $pairs[] = array($split[$i], $split[$i+1]);

    foreach ($pairs as $bits) {
        if ($bits[0] == "apply") {
            $this->apply($bits[1]); //Set result equal to apply.
            $this->queue[] = "output";
        } else {
            $this->queue[] = $bits; //Set the queue item as an array of (command, value).
        }
    }
    //var_dump($this->queue);
    //die;
    // lets process commands
    foreach ($this->queue as $index => $cmd) {
        if ($cmd == "output") {
            echo "Answer: " .$this->result;
            return;
        } else {
            switch($cmd[0]) {
                case "add":
                    $this->add($cmd[1]);
                    break;
                case "subtract":
                    $this->subtract($cmd[1]);
                    break;
                case "multiply":
                    $this->multiply($cmd[1]);
                    break;
                case "divide":
                    $this->divide($cmd[1]);
                    break;
                default:
                    echo "Unknown command!";
                    break;
            }
        }
    }
}

public function apply($number) {
    // manipulate $result, $queue, $number
    $this->result = $number;

}

public function add($number) {
    // manipulate $result, $queue, $number
    $this->result += $number;

}

public function subtract($number) {
    // manipulate $result, $queue, $number
    $this->result -= $number;

}

public function multiply($number) {
    // manipulate $result, $queue, $number
    $this->result *= $number;
}

public function divide($number) {
    // manipulate $result, $queue, $number
    $this->result /= $number;
}

} 
?>