PHP 计算器

header("Content-type:text/html;charset=utf-8");
        function deleteHtml($str) 
	{ 
	        $str = trim($str); 
		$str = strip_tags($str, ""); 
		$str = ereg_replace("	", "", $str); 
		$str = ereg_replace("
", "", $str); 
		$str = ereg_replace("
", "", $str); 
		$str = ereg_replace("
", "", $str); 
		$str = ereg_replace(" ", "", $str); 
		return trim($str); 
	}
	/*
	 * 将中缀表达式转换成后缀表达式
	 * 也就是逆波兰式
	 */
	class math_rpn
	{
		private $expression = array();   //需要转换的中缀表达式
		private $rpnexp = array();		//处理后的逆波兰式
		private $stack = array('#');   //储存临时运算符栈
		private $priority = array('#'=>0, '('=>10, '+' => 20, '-'=>20, '*'=>30, '/'=>30); //运算符优先级
		private $operator = array('(', '+', '-', '*', '/', ')'); //四则运算符
		public function __construct($expression)
		{
			$this->_init($expression);
		}
		private function get_token_array($string)
		{
			/* 构造记号流*/
			$token = array();
			$str_len = 0;
			while (true)
			{
				if (1 === preg_match('/^([%,\^\+\-\*\/\(\)]).*$/',$string,$sub))
				{
					array_push($token,$sub[1]);
					$string = substr($string,strlen($sub[1]));
					$str_len += strlen($sub[1]);
					continue;
				}
				elseif (1 === preg_match('/^(([0-9]+[\.]?[0-9]*)|([0-9]*[\.]?[0-9]+)).*$/',$string,$sub))
				{
					array_push($token,floatval($sub[1]));
					$string = substr($string,strlen($sub[1]));
					$str_len += strlen($sub[1]);
					continue;
				}
				elseif (1 === preg_match('/^([a-zA-Z_][0-9a-zA-Z_]*\().*$/',$string,$sub))
				{
					array_push($token,$sub[1]);
					$string = substr($string,strlen($sub[1]));
					$str_len += strlen($sub[1]);
					continue;
				}
				elseif (1 === preg_match('/^(\s+).*$/',$string,$sub))
				{
					$string = substr($string,strlen($sub[1]));
					$str_len += strlen($sub[1]);
					continue;
				}
				else 
				{
					break;
				}
			}
			if ($string != '') 
			{
				return $str_len;
			}
			return $token;
		}
		private function _init($expression)
		{
			$exp = array();
			$expression = deleteHtml($expression); 
			$exp = $this->get_token_array($expression);
			if(!is_array($exp))
			{
				$str = substr($expression, $exp,1);
				echo $expression,'表达式错误在',$str;
				exit;
			}
			$this->expression = $exp;
		}
		public function exp2rpn()
		{
			$count = count($this->expression);
			for($i = 0; $i<$count; $i++)
			{
				$char  = $this->expression[$i]; //获取表达式中的每一个字符串
				if ($char == '(') //如果字符为(,则直接存入$stack的栈顶
				{
					$this->stack[] = $char;
					continue;
				}
				else if (!in_array($char, $this->operator)) //如果字符不为运算符，则压入$rpnexp中
				{
					$this->rpnexp[] = $char;
					continue;
				}
				else if ($char == ')') //在$stack中查找最近"("之间的运算符，逐个出栈.送入栈$rpnexp中
				{
					for ($j =count($this->stack); $j >= 0; $j++)
					{
						$tmp = array_pop($this->stack);
						if ($tmp == '(') //跳出循环
							break;
						else
							$this->rpnexp[] = $tmp;
					}
					continue;
				}
				else if ($this->priority[$char] <= $this->priority[end($this->stack)])
				{
					$this->rpnexp[] = array_pop($this->stack);
					$this->stack[] = $char;
					continue;
				}
				else
				{
					$this->stack[] = $char;
					continue;
				}
			}
			//将存在临时的运算符栈剩余的内容存入rpnexp栈中
			for($i=count($this->stack); $i>=0; $i++)
			{
				if(end($this->stack) == '#')
					break;
				else
					$this->rpnexp[] = array_pop($this->stack);
			}
			return $this->rpnexp;
		}
		public function getResult($rpnexp)
		{
			$result = array();
			$rpnexp = array_reverse($rpnexp); //将值倒叙
			$count = count($rpnexp);
			//如果有运算符就计算，否则将数据压入$result结果栈中
			while($count>0)
			{
				$v = array_pop($rpnexp); 
				if(in_array($v, $this->operator))
				{
					$a = array_pop($result);
					$b = array_pop($result);
					switch($v)
					{
						case '+':
							array_push($result, ($a+$b));
							break;
						case '-':
							array_push($result, ($b-$a));
							break;
						case '*':
							array_push($result, ($a*$b));
							break;
						case '/':
							array_push($result, ($b/$a));
							break;
						default:
							break;
					}
				}
				else
					array_push($result, $v);
				$count--;
			}
			return array_pop($result);
		}
	}	
	$exp = "(30+3.1)*5/2-2";
	$mathrpn = new math_rpn($exp);
	$rpnExp = $mathrpn->exp2rpn();
	echo $mathrpn->getResult($rpnExp);//80.75 
?>