折半查找法（数列已升序）

#include <iostream>
using namespace std;

int BinarySearch(const int a[], int key, int low, int high); // 折半查找 
const int ArSize = 100;

int main()
{
	int a[ArSize];
	for (int i = 0; i < ArSize; i++)
	{
		a[i] = i * i + 1;
		cout << a[i] << ((i + 1)%10 == 0 ? "\n" : " ");
	}
	char ch;
	int searchkey;
	cout << "Please enter a number to be checked:\n";
	while (cin >> searchkey)
	{
	
		int b = BinarySearch(a, searchkey, 0, ArSize - 1);
	
		if (b != -1)
			cout << "It's a["<< b <<"]\n";
		else
			cout << "cannot found!\n";
			
		cout << "Do you want to continue?(Y/N)";
		cin >> ch;
		if (ch == 'N' || ch == 'n')
			break;
			
		cout << "Please enter a number to be checked:\n";
	}
	return 0;
}

int BinarySearch(const int a[], int key, int low, int high) // 折半查找 
{
	int middle;
	while (low <= high)
	{
		middle = (low + high)/2;
		if (key == a[middle])
			return middle;
		else if (key < a[middle])
		{
			high = middle - 1;
		}
		else
		{
			low = middle + 1;
		}
	}
	return -1; // not found!
}#include <iostream>
using namespace std;