A complete working C program to demonstrate all insertion methods on Linked List

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

// A linked list node
struct node
{
int data;
struct node *next;
};

/* Given a reference (pointer to pointer) to the head of a list and
an int, inserts a new node on the front of the list. */
void push(struct node** head_ref, int new_data)
{
    /* 1. allocate node */
    struct node* new_node = (struct node*) malloc(sizeof(struct node));

    /* 2. put in the data */
    new_node->data = new_data;

    /* 3. Make next of new node as head */
    new_node->next = (*head_ref);

    /* 4. move the head to point to the new node */
    (*head_ref) = new_node;
}

/* Given a node prev_node, insert a new node after the given
prev_node */
void insertAfter(struct node* prev_node, int new_data)
{
    /*1. check if the given prev_node is NULL */
    if (prev_node == NULL)
    {
    printf("the given previous node cannot be NULL");
    return;
    }

    /* 2. allocate new node */
    struct node* new_node =(struct node*) malloc(sizeof(struct node));

    /* 3. put in the data */
    new_node->data = new_data;

    /* 4. Make next of new node as next of prev_node */
    new_node->next = prev_node->next;

    /* 5. move the next of prev_node as new_node */
    prev_node->next = new_node;
}

/* Given a reference (pointer to pointer) to the head
of a list and an int, appends a new node at the end */
void append(struct node** head_ref, int new_data)
{
    /* 1. allocate node */
    struct node* new_node = (struct node*) malloc(sizeof(struct node));

    struct node *last = *head_ref; /* used in step 5*/

    /* 2. put in the data */
    new_node->data = new_data;

    /* 3. This new node is going to be the last node, so make next of
        it as NULL*/
    new_node->next = NULL;

    /* 4. If the Linked List is empty, then make the new node as head */
    if (*head_ref == NULL)
    {
    *head_ref = new_node;
    return;
    }

    /* 5. Else traverse till the last node */
    while (last->next != NULL)
        last = last->next;

    /* 6. Change the next of last node */
    last->next = new_node;
    return;
}

// This function prints contents of linked list starting from head
void printList(struct node *node)
{
while (node != NULL)
{
    printf(" %d ", node->data);
    node = node->next;
}
}

/* Driver program to test above functions*/
int main()
{
/* Start with the empty list */
struct node* head = NULL;

// Insert 6. So linked list becomes 6->NULL
append(&head, 6);

// Insert 7 at the beginning. So linked list becomes 7->6->NULL
push(&head, 7);

// Insert 1 at the beginning. So linked list becomes 1->7->6->NULL
push(&head, 1);

// Insert 4 at the end. So linked list becomes 1->7->6->4->NULL
append(&head, 4);

// Insert 8, after 7. So linked list becomes 1->7->8->6->4->NULL
insertAfter(head->next, 8);

printf("\n Created Linked list is: ");
printList(head);

return 0;
}

Output:

 Created Linked list is:  1  7  8  6  4