Linked list Insertion / Creating linked list

Today we are starting linked . and the simplest program of linked is inserting element in a linked list . there can be various insertion elements anywhere in linked list and can also create new one . i am discussing three methods 
1> if you want to add element at end of linked list 
2> you wanted to add the element at first position means opposite to first one . 
3> suppose you are giving the pointer of previous node where you want to insert element 

for this i used three different functions respectively 
1> append ()
2> push()
3> insert_after()

#include<stdio.h>
struct node
{
    int data;
    struct node* next;
};

void main()
{
    struct node* head = NULL;
    append(&head,7); /*append is a function that will add the node at end */
    append(&head,6);
    push(&head,9);  /*push will add the element on head */
    insert_after(head->next->next, 43);
    push(&head, 64);
    output(head);
}

void append(struct node** m, int value) /*  m is a pointer that is storing the address of head  */
{
    struct node* temp = (struct node*)malloc(sizeof(struct node));
    temp->data=value;
    temp->next= NULL;
    struct node *current = *m ; /*  (*m) means that value at the head as m was storing the address of head )*/
       /*current has same value now that of head */
    if(*m == NULL)
    {
        *m = temp;
    }

    else
    {
        while(current ->next!= NULL)
        {
            current=current->next;
        }
        current->next=temp;
    }
}

 void push(struct node **m , int value )
{
    struct node* temp = (struct node*)malloc(sizeof(struct node));
    temp->data=value;
    temp->next = *m; /* (*m) means that value at the head as m was storing the address of head )*/
    *m= temp; /*head will change by this */

}

void insert_after(struct node *prev_node,int value)
{
    if (prev_node== NULL)
    {
        printf("previous node can't be null");
        return;
    }
    else
    {
        struct node* temp = (struct node*)malloc(sizeof(struct node));
        temp->data=value;
        temp->next      =    prev_node->next ;
        prev_node->next =    temp;

    }

}

void output(struct node* current)
{
    while(current!=NULL)
    {
        printf("%d\n",current->data);
        current=current->next;
    }

}

the following picture will explain the pointers used in append function 

and this picture will explain the insert_after function