Insertion in LL

#include<stdio.h>
#include<stdlib.h>
struct node
{
    int data;
    struct node *next;
};
int main()
{
    struct node *head = NULL;
    append(&head,8);
    append(&head,7);
    push(&head,3);
    push(&head,4);
    append(&head,5);
    insertAfter(head->next->next,1);
    printf("Linked List is:\n");
    print(head);
    return 0;
}
void push(struct node** ref, int newData)
{
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = newData;
    newNode->next = (*ref);
    (*ref) = newNode;
}
void insertAfter(struct node* prev,int newData)
{
    if(prev == NULL)
    {
    printf("the given previous node can't be null");
    return 0;
    }
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = newData;
    newNode->next = prev->next;
    prev->next = newNode;
}
void append(struct node** ref, int newData)
{
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    struct node *last = *ref;
    newNode->data = newData;
    newNode->next = NULL;
    if(*ref == NULL)
    {
    (*ref)=newNode;
    return;
    }
    while(last->next != NULL)
    {
    last=last->next;
    }
    last->next = newNode;
    return 0;
}
void print(struct node *n)
{
    while(n!= NULL)
    {
    printf("%d",n->data);
    n=n->next;
    }
}