定義一個數組，設定它的左右下標，同時定義一箇中間下標mid，每次進行折半查詢，若要查詢的數比mid小，則右下標等於mid-1，若要查詢的數比mid大，則左下標等於mid+1。若要查詢的數等於mid，則迴圈停止。

#include<stdio.h>
#include<string.h>
int main()
{
	int arr[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	int k = 7;
	int left = arr[0];
	int right = sizeof(arr) / sizeof(arr[0]) - 1;
	while (left<=right)
	{
		int mid = left + (right - left) / 2;
		if (arr[mid] == k)
		{
			printf("找到了,下標為：%d\n",mid);
			break;
		}
		else if (arr[mid] <= k)
		{
			left = mid + 1;
		}
		else
		{
			right = mid - 1;
		}
	}
	if (left > right)
	{
		printf("沒有找到\n");
	}
	system("pause");
	return 0;
}
 

       若將折半查詢法定義為一個函式

       則具體程式碼如下：

#include <stdio.h>
#include <string.h>
int binary_search(int arr[], int k,int sz)
{
	int left = 0;
	int right = sz;
	while (left <= right)
	{
		int mid = left + (right - left) / 2;
		if (arr[mid] == k)
		{
			return mid;
		}
		else if (arr[mid] <= k)
		{
			left = mid + 1;
		}
		else
		{
			right = mid - 1;
		}
	}
	if (left > right)
	{
		return -1;
	}
}
int main()
{
	int arr[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	int k = 7;
	int left = 0;
	int sz = sizeof (arr) / sizeof (arr[0]) - 1;
	int right = sz;
	int ret = binary_search(arr, k, sz);
	if (ret == -1)
	{
		printf("沒有找到\n");
	}
	else
	{
		printf("找到了，下標為：%d\n",mid);
	}
	system("pause");
	return 0;
}