二分查找

二分查找就是折半查找，主要思想：
将要查找的数与表的中间的元素进行比较，若该数与中间值相等那么查找成功；如果该数大于中间的数，那么这个数一定在右子表中，继续对右子表进行折半查找；若该数比中间值小，那么这个数一定在左子表中，继续对左子表进行差找。知道查找成功或查找失败。
二分查找的函数代码如下：
void binary_search(int arr[], int size, int key)
{
int low, high, mid,count=0,count1=0;
low = 0;
high = size - 1;
while (low <= high)
{
count++;//record for number;
mid = (low + high) / 2;
if (key > arr[mid])
{
low = mid + 1;
}
else if (key < arr[mid])
{
high = mid - 1;
}
else if (key == arr[mid])
{
count1++;
printf("success!\nsearch %d times!arr[%d]=%d", count, mid, key);
break;
}
}
if (count1 == 0)
printf("no found!");
}
主函数代码如下：
int main()
{
int arr[100],key ,n, i;
printf("please input the length of array:\n");
scanf("%d", &n);
printf("please input element:\n");
for (i = 0; i < n;i++)
scanf("%d", &arr[i]);
printf("please input the number which do you want to search:\n");
scanf("%d", &key);
binary_search(arr, n, key);
printf("\n");
system("pause");
return 0;
}