Stack implemented as a linked list

#include<stdio.h>
#define max 4
struct node
{
        int data;
        struct node *next;
};
void push(struct node **,int);
void pop(struct node **);
void display(struct node *);
main()

{

        struct node *head;
        head = NULL;
        push(&head,10);
        push(&head,20);
        push(&head,30);
        push(&head,40);
        push(&head,50);
        display(head);
        pop(&head);
        printf("\nafter poping the element the stack is\n");
        display(head);
}
void push(struct node **q,int num)
{
        struct node *temp,*r;
        static int n=1;
        temp = *q;
        if(n<=max)
        {
                temp = (struct node*)malloc(sizeof(struct node));
                temp->data = num;
                temp->next = *q;
 *q = temp;
                n++;
        }
        else
        {
                printf("stack is full\n");
        }
}
void pop(struct node **q)
{
        struct node *temp,*old;
        temp = *q;
        if(temp == NULL)
        {
                printf("stack is empty\n");
        }
        else
        {
        *q = temp->next;
        free(temp);
        }
}
void display(struct node *q)
{
        while(q!=NULL)
        {
                printf("%d  ",q->data);
                q = q->next;
        }
}
-------------------------------------------------------------------------------------------------------------------------------------------
op :
stack is full
40  30  20  10
after poping the element the stack is
30  20  10