Automatically solve arithmetic problems - give it to your son to practice quick calculations o(∩_∩)o

Custom range, custom operator, custom number of operations. So cool

/**
 * Description of QuestionEngine
 * A question engine
 *
 * @author lyc
 * @copyright (c) 2013, Unary Inc.
*/
class QuestionEngine {

 /**
 * Question scope
 * @var string $scope
*/
 public $scope = array(1, 100);

 /**
 * Operators included, if there are multiple operators, the question will be mixed
 * @var string $operators
*/
 public $operators = '+-';

 /**
 * Number of operations
 * @var int
*/
 public $optTimes = 1;

 public function generate() {
 //Generate a set of values ​​​​according to the number of operations
 start:
 for ($index = 0; $index < $this->optTimes + 1; $index++) {
 $elements[] = $this->randomValue();
 }
 $operatorType = strlen( $this->operators); //There are several operators to choose from
 //Start assembling the calculation
 $question = '';
 for ($index = 0; $index < count($elements); $index++ ) {
 $question.=' ' . $elements[$index] . ' '; //Put a number in
 if ($index < count($elements) - 1)//If it is not the last number, Add an operator at the end
 $question.=substr($this->operators, mt_rand(0, $operatorType - 1), 1);
 }

 eval('$anwser = ' . $question . '; ');
 if ($anwser < 0) { //Exclude the case where the result is a negative number
 $elements = array();
 goto start; //Requires PHP5.3 support
 }

 echo "$question= " . $anwser;
 }

 /**
 * Generate a random value within a range
 *
 * @return int
*/
 protected function randomValue() {
 return mt_rand($this->scope[0], $this->scope[1]);
 }

}

include 'QuestionEngine.class.php';
$hello = new QuestionEngine();
$hello->generate();
?>

Result: 26 + 85 = 111