从中缀向后缀转换表达式

C实现

#include "stdio.h"
#include "string.h"
#include "stdlib.h"
typedef struct stack
{
  char *base;
  char *top;
} stack;
int pre(char sign)
{
  switch (sign)
     
    {
    case '+':
    case '-':
        return 1;
        break;
    case '*':
    case '/':
        return 2;
        break;
    case '^':
        return 3;
        break;
    default:
        return 0;
        break;
       
    }
}
int main()
{
  stack sign;
  int n, i;
  char expre[100];
  scanf("%d", & n);
  while (n--)
     
    {
        sign.base = (char *)malloc(100 * sizeof(char));
        sign.top = sign.base + 1;
        *sign.base = '#';
        scanf("%s", expre);
        for (i = 0; expre[i] != '#'; i++) 
      {
           if (expre[i] == '(') 
        {
              *sign.top++ = expre[i];
             
        }
           else if (expre[i] == ')')
        {
              while (*(sign.top - 1) != '(') 
          {
                 printf("%c", * (sign.top - 1));
                 sign.top--;
                
          }
              sign.top--;
             
        }
           else if (expre[i] == '+' || expre[i] == '-' || expre[i] == '*' || expre[i] == '/' || expre[i] == '^')
        {
              while (((*(sign.top - 1) == expre[i]) && (expre[i] == '^')) ? (pre(*(sign.top - 1)) > pre(expre[i])) : (pre(*(sign.top - 1)) >= pre(expre[i]))) 
          {
                 printf("%c", * (sign.top - 1));
                 sign.top--;
                
          }
              *sign.top++ = expre[i];
             
        }
           else printf("%c", expre[i]);
          
      }
        while (sign.top != sign.base + 1) 
      {
           printf("%c", * (sign.top - 1));
           sign.top--;
          
      }
        printf("\n");
       
    }
  return 0;
}