Circular buffer implementation using linked list

I'm a beginner with C. The below is the implementation of circular buffer using linked list. Please review my code and suggest any improvements to make it efficient or to improve in coding style.

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

struct link_list
{
    int item;
    struct link_list *next;
};

struct link_list *read=NULL;
struct link_list *write=NULL;
int size=NULL; //buffer size
static int p_size=0; //present size of buffer

void enqueue()
{
    int value;
    struct link_list *newnode=(struct link_list*)malloc(sizeof(struct link_list));
    printf("Enter new value : \n");
    scanf("%d",&value);
    newnode->item=value;
    newnode->next=NULL;

    if(read==NULL&&write==NULL)
    {
    read=write=newnode;
        p_size++;
    }
    else
    {   
        if (p_size<size)
        {
            printf("still buffer not filled\n");
            write->next=newnode;
            write=newnode;
            p_size++;
        }
        else
        {
            printf("size is exceeded\n");
            write=write->next;
            read->item=value;
            read=read->next;
        }
        write->next=read;
    }
    write->next=read;
}


void dequeue()
{
    int val;
    struct link_list *ptr=read;
    if(read==NULL)
    {
        printf("Stack is empty \n");
    }
    else
    {
        if (p_size>0)
        {   
            val=read->item;
            read=read->next;
            free(ptr);
            p_size--;
            printf("removed %d\n",val);
        }
        else 
        {
            p_size=0;
            read=write=NULL;
            printf("nothing else to remove\n");
        }
    }   
}


void print()
{
    printf("psize= %d\n",p_size);
    struct link_list *ptr=read;
    if (read==NULL)
    {
        printf("nothing in queue\n");return;
    }
    if (p_size==0) 
    {
        printf("stack empty\n");
        return;
    }
    else
    {
        while (ptr!=NULL)
        {
            if (ptr!=write)
            {
                printf("Value= %d Aderss= %p Next Address= %p\n", ptr->item,ptr, ptr->next);
                ptr=ptr->next;
            }
            else
            {
                printf("Value= %d Aderss= %p Next Address= %p\n", ptr->item,ptr, ptr->next);
                break;
            }
        }
        printf("read--@Value= %d Aderss= %p Next Address= %p\n", read->item,read, read->next);
        printf("write--@Value= %d Aderss= %p Next Address= %p\n", write->item,write, write->next);

    }
}


void main()
{
    char ch;
    int val;
    int loop=1;
    printf("enter the buffer size---\n");
    scanf("%d",&size);
    while(loop==1)
    {
        printf("select a) to add to queue, b) to dequeue s) sort p) print x)ext\n");
        scanf("%c",&ch);
        switch(ch)
        {
            case 'a':
                enqueue();
                break;
            case 'b':
                dequeue();
                break;
            case 'p':
                print();
                break;
            case 'x':
                loop=0;
                break;
        }
    }
}