用PHP实现的四则运算表达式计算实现代码

PHP实现：
代码如下:

1. <?php
   
2. /**
   
3. * 计算四则运算表达式
   
4. */
   
5. error_reporting(E_ALL);
   
6. $exp = '(1+2*(3+5)/4)*(3+(5-4)*2)';
   
7. $arr_exp = array();
   
8. for($i=0;$i<strlen($exp);$i++){
   
9. $arr_exp[] = $exp[$i];
   
10. }
    
11. $result = calcexp( array_reverse($arr_exp) );
    
12. echo $exp . '=' . $result;
    
13. function calcexp( $exp ){
    
14. $arr_n = array();
    
15. $arr_op = array();
    
16. while( ($s = array_pop( $exp )) != '' ){
    
17. if( $s == '(' ){
    
18. $temp = array(); $quote = 1; $endquote = 0;
    
19. while( ($t = array_pop($exp)) != '' ){
    
20. if( $t == '(' ){
    
21. $quote++;
    
22. }
    
23. if( $t == ')' ){
    
24. $endquote++;
    
25. if( $quote == $endquote ){
    
26. break;
    
27. }
    
28. }
    
29. array_push($temp, $t);
    
30. }
    
31. $temp = array_reverse($temp);
    
32. array_push($arr_n, calcexp($temp) );
    
33. }else if( $s == '*' || $s == '/' ){
    
34. $n2 = array_pop($exp);
    
35. if( $n2 == '(' ){
    
36. $temp = array(); $quote = 1; $endquote = 0;
    
37. while( ($t = array_pop($exp)) != '' ){
    
38. if( $t == '(' ){
    
39. $quote++;
    
40. }
    
41. if( $t == ')' ){
    
42. $endquote++;
    
43. if( $quote == $endquote )
    
44. break;
    
45. }
    
46. array_push($temp, $t);
    
47. }
    
48. $temp = array_reverse($temp);
    
49. $n2 = calcexp($temp);
    
50. }
    
51. $op = $s;
    
52. $n1 = array_pop($arr_n);
    
53. $result = operation($n1, $op, $n2);
    
54. array_push($arr_n, $result);
    
55. }elseif( $s == '+' || $s == '-' ){
    
56. array_push($arr_op, $s);
    
57. }else{
    
58. array_push($arr_n, $s);
    
59. }
    
60. }
    
61. $n2 = array_pop($arr_n);
    
62. while( ($op = array_pop($arr_op)) != '' ){
    
63. $n1 = array_pop($arr_n);
    
64. $n2 = operation($n1, $op, $n2);
    
65. }
    
66. return $n2;
    
67. }
    
68. function operation( $n1, $op, $n2 ){
    
69. switch ($op) {
    
70. case '+':
    
71. return intval($n1) + intval($n2);
    
72. break;
    
73. case '-':
    
74. return intval($n1) - intval($n2);
    
75. break;
    
76. case '*':
    
77. return intval($n1) * intval($n2);
    
78. break;
    
79. case '/':
    
80. return intval($n1) / intval($n2);
    
81. break;
    
82. }
    
83. }
    

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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。