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  1. #include <stdio.h>
  2. #include <ctype.h>
  3.  
  4. int top_p = 0;
  5. int top_s = 0;
  6.  
  7. void
  8. push_p(char *s, int c)
  9. {
  10.     s[top_p] = c;
  11.     top_p++;
  12. }
  13.  
  14. void
  15. push_s(char *s, int c)
  16. {
  17.     s[top_s] = c;
  18.     top_s++;
  19. }
  20.  
  21. int
  22. pop_p(char *s)
  23. {
  24.     top_p--;
  25.     return s[top_p];
  26. }
  27.  
  28. int
  29. pop_s(char *s)
  30. {
  31.     top_s--;
  32.     return s[top_s];
  33. }
  34.  
  35. void
  36. infix_to_postfix(char *in, char *post, char *stk)
  37. {
  38.     char operator[256] = {0};
  39.  
  40.     operator['('] = 0;
  41.     operator['+'] = 1;
  42.     operator['-'] = 1;
  43.     operator['*'] = 2;
  44.     operator['/'] = 2;
  45.     while (*in) {
  46.         if (isdigit(*in)) {
  47.             push_p(post, *in);
  48.         } else { /* Operator */
  49.             while (1) {
  50.                 switch (*in) {
  51.                     case '(':
  52.                         push_s(stk, *in);
  53.                         break;
  54.                     case ')':
  55.                         while (stk[top_s - 1] != '(') {
  56.                             push_p(post, pop_s(stk));
  57.                         }
  58.                         pop_s(stk);
  59.                         break;
  60.                     default:
  61.                         break;
  62.                 }
  63.                 if (*in == '(' && *in == ')') {
  64.                     break;
  65.                 }
  66. /* go here */
  67.                 if (!stk[top_s - 1]) {
  68.                     while (operator[stk[top_s - 1]] >= operator[*in]) {
  69.                         push_p(post, pop_s(stk));
  70.                         if (stk[top_s - 1]) {
  71.                             break;
  72.                         }
  73.                     }
  74.                 }
  75.                 break;
  76.             }
  77.             if (*in != '(' && *in != ')') {
  78.                 push_s(stk, *in);
  79.             }
  80.         }
  81.         in++;
  82.     }
  83. }
  84.  
  85. void
  86. stack_empty(char *post, char *stk)
  87. {
  88.     while (stk[top_s - 1]) {
  89.         push_p(post, pop_s(stk));
  90.     }
  91. }
  92.  
  93. int
  94. main(int argc, char **argv)
  95. {
  96.     char infix[] = "2*((3-5)*2)";
  97.     char postfix[256] = {0};
  98.     char stack[256] = {0};
  99.  
  100.     infix_to_postfix(infix, postfix, stack);
  101.     stack_empty(postfix, stack);
  102.     printf("%s\n", postfix);
  103.     return 0;
  104. }
Success #stdin #stdout 0s 2292KB
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Standard input is empty
stdout
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235-2**
https://ideone.com/hPvnFT
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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