Код к практике 3-1

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

struct node
{
        int value;
        struct node *next;
};

struct list
{
        struct node *head;
        struct node *tail;
};

void init(struct list* l)
{
        l->head = NULL;
        l->tail = NULL;
}

void clear(struct list* l)
{
        struct node* tmp1;
        struct node* tmp2;
        tmp1 = l->head;
        while (tmp1->next != NULL)
        {
                tmp2 = tmp1;
                tmp1 = tmp1->next;
                free(tmp2);
        }
        free(tmp1);
        init(l);
}
int isEmpty(struct list* l)
{
        if (l->head == NULL) return 0;
        else return 1;
}

struct node* find(struct list* l, int val)
{
        struct node* tmp;
        tmp = l->head;
        while (tmp->next != NULL)
        {
                if (tmp->value == val) return tmp;
                tmp = tmp->next;
        }
        return NULL;
}

struct node* findk(struct list* l, int n)
{
        int i = 1;
        struct node* tmp;
        tmp = l->head;
        for (i = 1; i < n; i++) tmp = tmp->next;
        return tmp;
}

int push_back(struct list*  l, int     val)
{
        struct node* new_node;
        new_node = (struct node*)malloc(sizeof(struct node));
        new_node->value = val;
        new_node->next = NULL;
        if (l->head == NULL) l->head = new_node;
        else if (l->head->next == NULL) l->head->next = new_node;
        else l->tail->next = new_node;
        l->tail = new_node;
        return 0;
}

int push_front(struct list* l, int val)
{
        struct node* new_node;
        new_node = (struct node*)malloc(sizeof(struct node));
        new_node->value = val;
        if (l->head == NULL)
        {
                new_node->next = NULL;
                l->tail = new_node;
        }
        else
                if (l->head->next == NULL) new_node->next = l->tail;
                else new_node->next = l->head;
        l->head = new_node;
        return 0;
}

int insertAfter(struct node* n, int val)
{
        struct node* new_node;
        new_node = (struct node*)malloc(sizeof(struct node));
        new_node->value = val;
        new_node->next = n->next;
        n->next = new_node;
        return 0;
}

int remova(struct list* l, int val)
{
        struct node* tmp1;
        struct node* tmp2;
        tmp1 = l->head;
        while (tmp1->value != val)
        {
                tmp2 = tmp1;
                tmp1 = tmp1->next;
        }
        if (tmp1 == l->head) l->head = tmp1->next;
        else if (tmp1 == l->tail)
        {
                tmp2->next = NULL;
                l->tail = tmp2;
        }
        else tmp2->next = tmp1->next;
        free(tmp1);
        return 0;
}

void print(struct list* l)
{
        if (isEmpty(l) == 1)
        {
                struct node* tmp;
                tmp = l->head;
                while (tmp->next != NULL)
                {
                        printf("%d ", tmp->value);
                        tmp = tmp->next;
                }
                printf("%d\n", l->tail->value);
        }
}

int main()
{
        int n, x, i, k1, k2, k3;
        struct list a;
        struct node* b;
        init(&a);
        scanf("%d", &n);
        for (i = 1; i <= n; i = i + 1)
        {
                scanf("%d", &x);
                push_back(&a, x);
        }
        print(&a);
        scanf("%d %d %d", &k1, &k2, &k3);
        b = find(&a, k1);
        if (b != NULL) k1 = 1;
                else k1 = 0;
        b = find(&a, k2);
        if (b != NULL) k2 = 1;
                else k2 = 0;
        b = find(&a, k3);
        if (b != NULL) k3 = 1;
                else k3 = 0;
        printf("%d%d%d\n", k1, k2, k3);
        scanf("%d", &x);
        push_back(&a, x);
        print(&a);
        scanf("%d", &x);
        push_front(&a, x);
        print(&a);
        scanf("%d %d", &n, &x);
        b = findk(&a, n);
        insertAfter(b, x);
        print(&a);
        scanf("%d", &x);
        remova(&a, x);
        print(&a);
        clear(&a);
        return 0;
}