#include<stdio.h>
#include<conio.h>
#include<alloc.h>
typedef struct pointer
         { int info;
           struct pointer *link;
         } ds;
ds *l,*q,*p,*k;
int a,n;
void init()
{
	l=NULL;
}
int ccs()
{
	if(n<=2) return 0;
	p=l;
	q=l;
	p=p->link;
	k=p->link;
	while(k!=NULL)
	{
		if(p->info!=(q->info+k->info)/2) return 0;
		q=q->link;
		p=p->link;
		k=k->link;
	}
	return 1;
}
int tang()
{
	q=l;p=l;
	p=p->link;
	while(p!=NULL)
	{
		if(q->info<p->info) return 0;
		q=q->link;
		p=p->link;
	}
	return 1;
}
main()
{
	int i;
	init();
	printf("nhap tu ban phim so phan tu cua danh sach \n");
	printf("khuyen cao : nen nhap tu` 3 phan tu? tro len . \n N=");
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	{
		p=(ds *)malloc(sizeof(ds));
		printf("phan tu thu %d ",i);
		scanf("%d",&p->info);
		p->link=l;
		l=p;
	}
	p=l;a=0;
	while(p!=NULL)
	{
		if(p->info>0) a++;
		p=p->link;
	}
	if(a==0) printf("danh sach khong co phan tu nao duong \n");
	else printf(" so phan tu duong co trong danh sach la :%d \n",a);
	if(ccs()==0) printf(" trong danh sach khong ton tai mot day so cap so cong \n ");
	else printf("danh sach ton tai mot day so cap so cong \n");
	if(tang()==0) printf("danh sach khong duoc sap sep tang \n");
	else printf("danh sach dc sap xep theo thu tu tang dan \n");
	getch();
}