Convertir notación infija a posfija.

inapos.c

#include <stdlib.h>

 typedef struct Nodo{
                        int  info;
                        struct Nodo *sig;
                       } *Pila;

     Pila empty(){
          return NULL;
          }

     Pila push(int e, Pila p){
          Pila t=(Pila)malloc(sizeof(struct Nodo));
          t->info=e;
          t->sig=p;

          return t;
          }

      int isempty(Pila p){
          return (p==NULL);
          }

      int top(Pila p){
          return (p->info);
          }

      Pila pop(Pila p){
          return (p->sig);
          }

      int esoperando(char);
      int esoperador(char);
      int precedencia(char);
      int esmayoroigual(int, int);


      char esizq(char);

int main(int argc, char *argv[])
{
      char *s,c;
      Pila p=empty();

      s=*++argv;

      while((c=*s++)!='\0'){
           if (esizq(c))
                p=push(c,p);
           else if (esoperando(c))
                printf("%c", c);
                else if (esoperador(c))
                        if (isempty(p)|| esizq(top(p)))
                             p=push(c,p);
                        else{
                           while(esmayoroigual(precedencia(top(p)),precedencia(c))){
                                printf("%c",top(p));
                                p=pop(p);
                           };
                           p=push(c,p);
                        }
                     else{
                          while(top(p)!='('){
                               printf("%c", top(p));
                               p=pop(p);
                          }
                          p=pop(p);
                     }
      }

      while(!isempty(p)){
           printf("%c",top(p));
           p=pop(p);
      }


            return 0;
}


char esizq(char c){
      return c=='(';
}

int esoperando(char a){
    return (a>='a' && a<='z')||(a>='A' && a<='Z')||(a>='0' && a<='9');
}

int esoperador(char a){
     return (a=='+'|| a=='-' || a=='*' || a=='/' || a=='!');
}

int precedencia(char a){
      switch (a){
          case '(': return 0; break;
          case '+': return 1; break;
          case '-': return 1; break;
          case '*': return 2; break;
          case '/': return 2; break;
          case '!': return 3; break;
      }
}

int esmayoroigual(int x, int y){
      return (x>=y);
}