对分查找
//BinarySearch.h

#include "BinarySearch.h"int main(void){int array[] = {1,2,3,4,5,6,7,8,9,10,11};int size = sizeof(array)/sizeof(*array);int x = 5;int index = BinarySearch(array, x, size);printf("the index is %d\n",index);return 0;}

//前提是升序
思路：折半比较，array[mid]小于x说明在mid的右侧，将下限置mid+1，array[mid]大于x说明在mid的左侧，将上限置mid-1；其中的现在条件就是low<=high.