gistfile1.txt

<?php
class Test extends PHPUnit_Framework_TestCase {

    private $calc;

    protected function setUp()
    {
        $this->calc = new Calc();
    }
    public function test_i_have_calc()
    {
        $this->assertInstanceOf('Calc', $this->calc);
    }

    public function test_sums_2_strings()
    {
        $this->assertSame(2, $this->calc->calculate('1 + 1'));
    }

    public function test_minus_2_strings()
    {
        $this->assertSame(1, $this->calc->calculate('2 - 1'));
    }

    public function test_minus_2_strings2()
    {
        $this->assertSame(-4, $this->calc->calculate('2 - 6'));
    }

    public function test_multiply_2_strings()
    {
        $this->assertSame(15, $this->calc->calculate('3 * 5'));
    }

    public function test_divide_2_strings()
    {
        $this->assertSame(3, $this->calc->calculate('6 / 2'));
    }
    public function test_multiple_operands()
    {
        $this->assertSame(2, $this->calc->calculate('6 + 2 - 6'));
    }

    public function test_operator_position()
    {
        $this->assertSame(6, $this->calc->calculate('2 + 2 * 2'));
    }

    public function test_operator2_position()
    {
        $this->assertSame(6, $this->calc->calculate('2 +2*2'));
    }

}

class Calc
{
    public function calculate($string)
    {
        $arr = $this->stringParser($string);
        $result = $arr[0];
        $primary = array('*', '/');
        // Multiples and divisions
        for($i = 1; $i < count($arr); $i = $i + 2) {
            if(in_array($arr[$i], $primary)) {
                $result = $this->_makeAction($result, $arr[$i], $arr[$i+1]);
                unset($arr[$i]);
                unset($arr[$i+1]);
            }
        }
        // sums and minuses
        for($i = 1; $i < count($arr); $i = $i + 2) {
                $result = $this->_makeAction($result, $arr[$i], $arr[$i+1]);
        }
        return $result;
    }

    private function _makeAction($result, $action, $value)
    {
        switch ($action) {
            case '+':
                return $result + $value;
            case '-':
                return $result - $value;
            case '*':
                return $result * $value;
            case '/':
                return $result / $value;
        }
    }
    
    private function stringParser($string) {
        $data = array();
        $lastNumber = false;
        for($i = 0; $i < strlen($string); $i++) {
            if($string[$i] != ' ') {
                if(is_numeric($string[$i])) {
                    if($lastNumber)
                        $data[count($data)] .= $string[$i];
                    else {
                        $data[] = $string[$i];
                        $lastNumber = true;
                    }
                } else {
                    $data[] = $string[$i];
                    $lastNumber = false;
                }
            }
        }
        return $data;
    }
}