Code lập trình công nghệ thông tin

#include<stdio.h>
#include<conio.h>

struct node
{
int info;
struct node *next;
};
typedef node *listnode;
listnode *head;
void init(listnode *head)
{
*head=NULL;
}

void insert_first(listnode *head,int x)
{
listnode p;
p=new node;
p->info=x;
p->next= *head;
*head=p;
}

void insert_last(listnode *head,int x)
{
listnode p,q;


p=new node;
p->info=x;

p->next=NULL;
if(*head==NULL) *head=p;
else
{
q=*head;
while(q->next!=NULL)q=q->next;
q->next=p;
}
}
void delete_first(listnode *head)
{
listnode q;
if(*head!=NULL)
{
q=*head;
*head=q->next;
q->next=NULL;
delete(q);
}
}
void delete_last(listnode *head)
{
listnode q,r;
if((*head)->next==NULL)
{
delete_first(head);


return;
}

r=*head;
while(r->next!=NULL)
{
q=r;
r=r->next;
}
q->next=NULL;delete(r);
}
void output(listnode *head)
{
listnode p;
p=*head;
while(p!=NULL)
{
printf("%5d",p->info) ;
p=p->next;
}
}
int tong(listnode *head)
{
int t=0;
listnode p;
p=*head;
while(p!=NULL)
{


t+=p->info;
p=p->next;
} return t;

}
listnode search(listnode *head,int key)
{
listnode q;
q=*head;
while((q!=NULL)&&(q->info!=key)) q=q->next;
return q;
}
void main()
{
int chon,x,key;
listnode *head;
do
{
clrscr;
printf("\n 1 Nhap danh sach");
printf("\n 2 chen pt vao dau");
printf("\n 3 chen phan tu vao cuoi");
printf("\n 4 xoa pt cao dau");
printf("\n 5 xoa phan tu vao cuoi");
printf("\n 6 tinh tong");
printf("\n 7 tim key");
printf("\n 8 thoat");
printf("\n");
scanf("%d",&chon);


switch(chon)
{

case 1:
init(head);
break;
case 2:
printf("\nNhap x:");
scanf("%d",&x);
insert_first(head,x);
output(head);
break;
case 3:
printf("\nNhap x:");
scanf("%d",&x);
insert_last(head,x);
output(head);
break;
case 4:
delete_first(head);
output(head);
break;
case 5:
delete_last(head);
output(head);
break;
case 6:
output(head);


printf("\n Tong la %d",tong(head));
break;
case 7:

printf("\n nhap key:");
scanf("%d",&key);
output(head);
if((search(head,key)==NULL)) printf("\n ko tim thay %d",key);
else printf("\n tim thay %d",key);
break;
case 8:
break;
}
getch();
}
while(chon!=8);
}