c语言二分法

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3
 4 int Search(int *a,int key)
 5 {//在顺序表中折半查找key的元素，若找到返回元素下标，否则返回0
 6     int low=0,mid;
 7     int high=20;
 8     while(low<=high)
 9     {
10         mid=(low+high)/2;
11         if(key==a[mid]) return mid;    //找到待查元素
12         else if(key<a[mid]) high=mid-1;//继续在前半区查找
13         else low=mid+1;                //在后半区查找
14     }
15     return 0;                          //未找到
16 }
17
18 void main()
19 {
20     int *a,key,i;
21     int b[20]={0};
22     a=b;
23     printf("请输入从大到小的20个整数：\n");
24     for(i=1;i<=20;i++)
25     {
26         scanf("%d",&b[i]);
27
28     }
29     printf("\n");
30     printf("请输入你要查找的数：\n");
31     scanf("%d",&key);
32
33     if(!Search(a,key)) printf("要查找的数不在目标数组中！\n");
34     else printf("你要查找的数的序号是：%d \n",Search(a,key));
35 }