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

typedef struct Number {
    int num;
    struct Number *nxt;
} Number;


/* Adds a new element to the end of the list
 * Returns with the potentially modified head pointer
 * Usage:
 *   l = list_toend(l, 5);
 */
Number *list_toend(Number *list, int what) {
    Number *newel = (Number*) malloc(sizeof(Number));
    newel->num = what;
    newel->nxt = NULL;
    if (list == NULL)
        return newel;
    else {
        Number *iter;
        for (iter = list; iter->nxt != NULL; iter = iter->nxt)
            ; /* empty for loop */
        iter->nxt = newel;
        return list;
    }
}


/* Inserts a zero and the list element each time
* an even number is found in the list
*/
void list_202(Number *list) {
    for (Number *iter = list; iter != NULL; iter = iter->nxt)
        if (iter->num % 2 == 0) {
            Number *newnum, *newzero;
            newnum = (Number*) malloc(sizeof(Number));
            newnum->num = iter->num;
            newnum->nxt = iter->nxt;
            newzero = (Number*) malloc(sizeof(Number));
            newzero->num = 0;
            newzero->nxt = newnum;
            iter->nxt = newzero;
            /* jump over the newly inserted elements */
            iter = iter->nxt->nxt;
        }
}


void list_print(Number *list) {
    Number *iter;
    for (iter = list; iter != NULL; iter = iter->nxt)
        printf("%d ", iter->num);
    printf("\n");
}

void list_free(Number *list) {
    while (list != NULL) {
        Number *nxt = list->nxt;
        free(list);
        list = nxt;
    }
}


/* Main program. */
int main(void) {
    Number *list = NULL;
    int n;

    printf("Enter numbers (0 to finish): \n");
    scanf("%d", &n);
    while (n != 0) {
        list = list_toend(list, n);
        scanf("%d", &n);
    }

    list_print(list);
    list_202(list);
    list_print(list);

    list_free(list);

    return 0;
}