stack doubly hw

#include<stdio.h>
#include<stdlib.h>
typedef struct node
{
    int a;
    struct node *next,*prev;
} node;
node*head=NULL,*tail=NULL;
void PUSH(int aN)
{
    node*N=(node*)malloc(sizeof(node));
    N->a=aN;
    N->next=NULL;
    N->prev=NULL;

    if(head==NULL)
    {
        head=N;
        tail=N;
        return;
    }
    else
    {
        tail->next=N;
        N->prev=tail;
        N->next=NULL;
        tail=N;
        return;
    }

}

int POP()
{
    int a=0;
    node*list;
    if(head==NULL)
    {
        printf("empty");
    }
    else
    {
        node* temp;
        temp=tail;
        a=tail->a;
        tail->prev->next=NULL;
        tail = tail->prev;
        free(temp);

        return a;
    }
}

int main()
{
    int n,x,y,i,j,s=0;
    printf("ENTER PUSH CASE:");
    scanf("%d",&n);
    for(i=0; i<n; i++)
    {
        scanf("%d",&x);
        PUSH(x);
    }
   printf("ENTER POP CASE:");
    scanf("%d",&y);
    for(j=0; j<y; j++)
    {
        s=POP();
        printf("%d ",s);
    }
}