#include<stdio.h>
#include<stdlib.h>
#define N 10
typedef struct
{
int *elem;
int length;
}list;
list L;
int *head;
void initial_list()
{
L.length=N;
L.elem=NULL;
}
void create_list()
{
int i=0;
head=L.elem=(int *)malloc(N*sizeof(int));
   if(!L.elem)
    {
      printf("overflow!");
      exit(0);
    }
printf("please input the sequential list(%d):\n",N);
while(i<N)
   {
     printf("\nthe %dth elem:",i+1);
    scanf("%d",&(L.elem[  i ]));
   i++;
   }
getchar();
}
int issequential_list()
{
int i=0;
L.elem=head;
while(i<N-1)
{
  if(L.elem[  i ]>L.elem[  i+1 ])
     return 0;
i++;
}
return 1;
}
void search_key()
{
int key,i;
char ch;
while(1)
{
i=0;
printf("\nplease input the key:\n");
scanf("%d",&key);
getchar();
L.elem=head;
while(i<N)
{
   if(L.elem[  i ]==key)
    {
    printf("find it at %dth elem.\n",i+1);
    break;
    }
i++;
}
if(i==N)
printf("not find!\n");
printf("Are you want to continue search?Y or N?:");
scanf("%c",&ch);
getchar();
if(ch=='N'||ch=='n')
  break;
}
}
void devide_search_key(int start,int end,int e)
{
int n=(start+end)/2;
if(start==end)
{printf("\ncannot find !!");
return;
}
  if(L.elem[  n ]==e)
       {
        printf("\nfind it at the %dth elem",n+1);
        return;
        }
      else
      {
        if(L.elem[  n ]>e)
        devide_search_key(start,n,e);
        else
devide_search_key(n,end,e);
     }
return;
}





main()
{
int choice,key,start,end;
char ch;
clrscr();
printf("1.sequential search.\n 2.devide search.\n3.quit.\n");
printf("please choose the search method:");
scanf("%d",&choice);
printf("\n");
switch(choice)
{
case 1:
initial_list();
create_list();
search_key();
break;
case 2:
initial_list();
create_list();
while(1)
{
if(issequential_list())
  {
   while(1)
    {
  start=0;
  end=N-1;
  printf("\n please input the key:");
  scanf("%d",&key);
getchar();
  devide_search_key(start,end,key);
  printf("Are you want to continue search?Y or N?:");
  scanf("%c",&ch);
  getchar();
  if(ch=='N'||ch=='n')
goto loop;
   }
}
else
  {
printf("\nwhat you input is not sequential list.");
printf("\nplease create it again!");
  }
}
loop:
break;
case 3:
exit(0);
default:
printf("\nerror dut to the wrong input format!");
}
}

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