struct cella {
    char *token;
    struct cella *next;
};
typedef struct cella *ListaToken;

ListaToken tokenize(char *s) {
    ListaToken l;
    int i;
    while (s[i]){
        l = (ListaToken)malloc(sizeof(ListaToken));
        l->next = s[i];
        i++;
    }
    l->next = NULL;
    return l;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct cella {
    char *token;
    struct cella *next;
} *ListaToken;

ListaToken tokenize(const char *s) {
    ListaToken top = NULL, current, l;
    char *p, *tmps = strdup(s);

    for(p=strtok(tmps, " ");p;p=strtok(NULL, " ")){
        l = malloc(sizeof(*l));
        l->token = strdup(p);
        l->next = NULL;
        if(top == NULL){
            current = top = l;
        } else {
            current->next = l;
            current = l;
        }
    }
    free(tmps);
    return top;
}

void print(ListaToken l){
    while(l){
        printf(""%s" -> ", l->token);
        l = l->next;
    }
    printf("NULLn");
}
int main(){
    ListaToken list1, list2;
    list1 = tokenize("12 17 + 4 3 - /");
    print(list1);
    list2 = tokenize("12 17 + 4 - /");
    print(list2);

    return 0;
}

char *mystrdup(const char *s){
    char *dup = malloc(strlen(s) + 1);
    return strcpy(dup, s);
}

char *mystrtok_r(char *str, const char *delims, char **store){
    char *p, *wk;
    if(str != NULL){
        *store = str;
    }
    if(*store == NULL) return NULL;
    *store += strspn(*store, delims);//skip delimiter
    if(**store == '') return NULL;
    p=strpbrk(wk=*store, delims);
    if(p != NULL){
        *p='';
        *store = p + 1;
    } else {
        *store = NULL;
    }
    return wk;
}

char *mystrtok(char *str, const char *delimis){
    static char *store;
    return mystrtok_r(str, delimis, &store);
}

ListaToken tokenize(const char *s) {
    ListaToken top = NULL, current, l;
    const char *p = s, token[16];
    int len=0;
    while(1==sscanf(p, "%15s%n", token, &len)){
        l = malloc(sizeof(*l));
        l->token = malloc(len + 1);
        strcpy(l->token, token);
        p += len;
        l->next = NULL;
        if(top == NULL){
            current = top = l;
        } else {
            current->next = l;
            current = l;
        }
    }
    return top;
}