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。