用PHP实现的四则运算表达式计算

题目要求：有一个四则运算的字符串表达式，编写一个函数，计算四则运算的结果

PHP实现：

 1

 2

 3 /**

 4  * 计算四则运算表达式

 5  */

 6

 7 error_reporting(E_ALL);

 8

 9 $exp = '(1+2*(3+5)/4)*(3+(5-4)*2)';

10 $arr_exp = array();

11

12 for($i=0;$i

13     $arr_exp[] = $exp[$i];

14 }

15 $result = calcexp( array_reverse($arr_exp) );

16 echo $exp . '=' . $result;

17

18 function calcexp( $exp ){

19     $arr_n = array();

20     $arr_op = array();

21    

22     while( ($s = array_pop( $exp )) != '' ){

23         if( $s == '(' ){

24             $temp = array(); $quote = 1; $endquote = 0;

25             while( ($t = array_pop($exp)) != '' ){

26                 if( $t == '(' ){

27                     $quote++;

28                 }

29                 if( $t == ')' ){

30                     $endquote++;

31                     if( $quote == $endquote ){

32                         break;

33                     }

34                 }

35                 array_push($temp, $t);

36             }

37             $temp = array_reverse($temp);

38             array_push($arr_n, calcexp($temp) );

39         }else if( $s == '*' || $s == '/' ){

40             $n2 = array_pop($exp);

41             if( $n2 == '(' ){

42                 $temp = array(); $quote = 1; $endquote = 0;

43                 while( ($t = array_pop($exp)) != '' ){

44                     if( $t == '(' ){

45                         $quote++;

46                     }

47                     if( $t == ')' ){

48                         $endquote++;

49                         if( $quote == $endquote )

50                             break;

51                     }

52                     array_push($temp, $t);

53                 }

54                 $temp = array_reverse($temp);

55                 $n2 = calcexp($temp);

56             }

57            

58             $op = $s;

59             $n1 = array_pop($arr_n);

60            

61             $result = operation($n1, $op, $n2);

62             array_push($arr_n, $result);

63         }elseif( $s == '+' || $s == '-' ){

64             array_push($arr_op, $s);

65         }else{

66             array_push($arr_n, $s);

67         }

68     }

69    

70     $n2 = array_pop($arr_n);

71     while( ($op = array_pop($arr_op)) != '' ){

72         $n1 = array_pop($arr_n);

73         $n2 = operation($n1, $op, $n2);

74     }

75    

76     return $n2;

77 }

78

79 function operation( $n1, $op, $n2 ){

80     switch ($op) {

81         case '+':

82             return intval($n1) + intval($n2);

83             break;

84         case '-':

85             return intval($n1) - intval($n2);

86             break;

87         case '*':

88             return intval($n1) * intval($n2);

89             break;

90         case '/':

91             return intval($n1) / intval($n2);

92             break;

93     }

94 }

这个实现方式中使用了两个堆栈，一个用来存储数字，一个用来存储运算符，遇到括号以后就递归进入括号内运算，实现方式有点笨拙，后面补充一下“逆波兰表达式”的算法实现。