#include <iostream>
using namespace std;
// 用折半查找方法，在元素呈升序排列的数组list中查找值为key的元素
template <class T>
int binarySearch(T list[], int n, T key)
{
int mid, low, high;
T midvalue;
low=0;
high=n-1;
while (low <= high) // low <= high表示整个数组尚未查找完
{
mid = (low+high)/2; // 求中间元素的下标
midvalue = list[mid]; // 取出中间元素的值
if (key == midvalue)
return mid; // 若找到,返回下标
else if (key < midvalue)
high = mid-1;
// 若key < midvalue将查找范围缩小到数组的前一半
else
low = mid+1; // 否则将查找范围缩小到数组的后一半
}
return -1; // 没有找到返回-1
}
int main()
{
int i, n;
int data1[]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};
cout << "输入想查找的数字(1~20)：";
cin >> n;
cout << "数据为：" << endl;
for(i=0;i<20;i++)
cout << data1[i] << " ";
cout << endl;
i = binarySearch ( data1 , 20 , n );
if (i<0)
cout << "没有找到数字" << n << endl;
else
cout << n << "是第" << i+1 << "个数字" << endl;
return 0;
}
