Circular Linked List in C

#include stdio.h>
#include conio.h>
#include stdlib.h>
#include alloc.h>
#define null 0
struct node
{
int info;
struct node *link;
}*start;
void main()
{
int ch,n,m,position,i;
last=null;
while(1)
{
printf("1.create
2.addat
3.addbt
4.del
5.disp
6.exit
");
printf("er ur ch");
scanf("%d",&ch);
switch(ch)
{
case 1:
printf("er no of itc");
scanf("%d",&n);
for(i=0;i{
printf("er the element");
scanf("%d",&m);
create(m);
}
break;
case 2:
printf("er the element");
scanf("%d",&m);
addat(m);
break;
case 3:
printf("er the element");
scanf("%d",&m);

printf("er the position");
scanf("%d",&position);
addbt(m,position);
break;
case 4:
if(last==null)
{
printf("list is empty");
continue;
}
printf("er the element for delete");
scanf("%d",&m);
del(m);
break;
case 5:
disp();
break;
case 6:
exit(0);
break;
default:
printf("wrong choice");
}
}
}
create(int data)
{
struct node *q,*tmp;
tmp=(struct node *)malloc(sizeof(struct node));
tmp->info=data;
tmp->link=null;
if(last==null)
{
last=tmp;
tmp->link=last;
}
else
{
tmp->link=last->link;
last->link=tmp;
last=tmp;
}}


addat(int data)
{

struct node *q,*tmp;
tmp=(struct node *)malloc(sizeof(struct node));
tmp->info=data;
tmp->link=last->link;
last->link=tmp;
}
addbt(int data,int pos)
{
struct node *tmp,*q;
int i;
q=last->link;;
for(i=0;i{
q=q->link;
if(q==last->link)
{
printf("there r lessthan %d elements",pos);
return;
}
}
tmp=(struct node *)malloc(sizeof(struct node));
tmp->link=q->link;
tmp->info=data;
q->link=tmp;
if(q==last)
last=tmp;
}
del(int data)
{
struct node *tmp,*q;
if(last->link==last&&last->info==data)
{
tmp=last;
last=null;
free(tmp);
return;
}
q=last->link;

if(q->info==data)
{
tmp=q;
last->link=q->link;
free(tmp);
return;
}
while(q->link!=last)
{

if(q->link->info==data)
{
tmp=q->link;
q->link=tmp->link;
free(tmp);

printf("element %d is deleted",data);
}
if(q->link->info=data)
{
tmp=q->link;
q->link=last->link;
free(tmp);
last=q;
return;}
printf("element%d is not found",data);
}
disp()
{
struct node *q;
if(last==null)
{
printf("list isdempty");
return;
}q=last->link;
while(q!=last)
{
printf("%d",q->info);
q=q->link;
}
printf("%d",last->info);
}

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