折半查找<二分查找>

折半条件：必须在一个有序数组内进行。

例如：在一个数组中查找一个数，找到就输出该元素下标，如果没找到就输出-1:

#include<stdio.h>

#include<stdlib.h>

#include<string.h>

intbin_search(int*p,intx,int n)

{

                intleft = 0;

                intright = n - 1;

                while(left <= right)

                {

                                inti = 0;

                                i = ( right-left)/2+left;//(left&right) + ((left^right) >> 1)

                                                                  //right/2+left/2;

                                                                   //如果left和right很大，要防止left+right发生溢出

                                if(p[i] > x)

                                {

                                                right = i - 1;

                                }

                                elseif (p[i] < x)

                                {

                                                left = i + 1;

                                }

                                else

                                                returni;

                }

                return-1;

}

intmain()

{

                printf("请输入数组的大小:_");

                intn = 0;

                scanf("%d", &n);

                printf("请输入要查找的元素\n");

                intx = 0;

                scanf("%d", &x);

                int*p = (int*)calloc(n, sizeof(int));           //采用动态内存，提高对内存的利用

                if(p == NULL)

                {

                                printf("out of memory\n");

                                exit(1);

                }

                printf("请初始化数组\n");

                for(inti = 0; i < n; i++)

                {

                                scanf("%d", &p[i]);

                }

                intret=bin_search(p,x,n);

                printf("%d\n", ret);

                free(p);

                system("pause");

                return0;

}