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


typedef struct Word {
    char word[50 + 1];
    struct Word *nxt;
} Word;


/* Append new element to the end of the list.
 * Usage:
 *   words = list_toend(words, "apple");
 */
Word *list_toend(Word *list, char *word) {
    Word *newel = (Word*) malloc(sizeof(Word));
    strcpy(newel->word, word);
    newel->nxt = NULL;
    if (list == NULL)
        return newel;
    else {
        Word *iter;
        for (iter = list; iter->nxt != NULL; iter = iter->nxt)
            ; /* empty loop */
        iter->nxt = newel;
        return list;
    }
}


/* Deletes length 4 words from the list
 * Usage:
 *   words = delete_length4(words);
 */
Word *delete_length4(Word *list) {
    /* check if the list starts with a length 4 word */
    while (list != NULL && strlen(list->word) == 4) {
        Word *todelete = list;
        list = todelete->nxt;
        free(todelete);
    }

    /* then move on and check the rest */
    if (list != NULL) {
        Word *delayed = list;
        Word *iter = list->nxt;
     
        while (iter != NULL) {
            Word *next = iter->nxt;
     
            if (strlen(iter->word) == 4) {
                delayed->nxt = next;  /* 1 */
                free(iter);              /* 2 */
            } else
                delayed = iter;
            iter = next;                 /* 3 */
        }
    }

    return list;
}


/* Prints the words */
void list_print(Word *list) {
    Word *iter;
    for (iter = list; iter != NULL; iter = iter->nxt)
        printf("%s ", iter->word);
    printf("\n");
}


/* Releases the list */
void list_free(Word *list) {
    while (list != NULL) {
        Word *nxt = list->nxt;
        free(list);
        list = nxt;
    }
}


int main(void) {
    Word *list = NULL;
    char word[50 + 1];

    printf("Enter words! The last should be \"x\".\n I will delete all length-4 words.\n");

    scanf("%50s", word);
    while (strcmp("x", word) != 0) {
        list = list_toend(list, word);
        scanf("%50s", word);
    }

    list = delete_length4(list);
    list_print(list);

    list_free(list);

    return 0;
}