题目：使用二分查找，查找一个数是否存在于一个升序数组中

#include <stdio.h>int binarySearch(int arr[], int length, int elem);int main()
{int arr[] = { 2, 3, 4, 5, 6, 7, 8, 9, 10 };int key;int length = sizeof(arr) / sizeof(arr[0]);printf("请输入要查找的元素：\n");scanf_s("%d", &key);int mid = binarySearch(arr, length, key);if (mid != -1) {printf("找到了该数， 数组下标为：%d", mid);}else {printf("未找到该数");}return 0;
}int binarySearch(int arr[], int length, int elem) {int low = 0, high = length - 1, mid;while (low <= high) {mid = (low + high) / 2;if (arr[mid] == elem) {return mid;}else if (arr[mid] > elem) {high = mid - 1;}else {low = mid + 1;}}return -1;  //未找到
}