二分法

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int paixu(int *a);
int chazhao(int *a,int b);


int main()
{
    int a[10] = { 2, 56, 58, 685, 459, 32, 1, 52, 68, 45 };
    paixu(a);
    int xiabiao = 0;
    xiabiao = chazhao(a, 685);
    printf("%d
", xiabiao);
    return 0;
}

int paixu(int *a)
{
    int len = sizeof(a);
    for (int i = 0; i < len; i++)
    {
        for (int j = 0; j < len - 1; j++)
        {
            if (a[j] < a[j + 1])
            {
                int tmp = a[j];
                a[j] = a[j + 1];
                a[j + 1] = tmp;
            }
        }
    }
}

int chazhao(int *a, int b)    //b为想查找的数据
{
    //下标
    int xiabiao = 0;
    //区域下限
    int low = 0;
    //区域上限 初次上限取为数组的最大宽度
    int high = sizeof(a);
    //二分法取得中间值
    int middle;

    while (high > low)
    {
        //一开始中间值为数组的中间
        middle = (low + high) / 2;
        //判断直到当b等于中间值时 输出中间值的下标
        if (b == a[middle])
        {
            return middle;
        }
        //进行循环时 如果b小于中间值 则更改上限，把刚才的中间值变为上限
        if (b < a[middle])
        {
            high = middle-1;
        }
        //如果b>中间值，则更改下限
        if (b >a[middle])
        {
            low = middle+1;
        }
    }
}

思路：

　　取数组的首位下标作为上下限

　　取其中间值作为基准

　　用待查找值和中间值所对应的数字对比

　　如果不相等，则判断大小，并且重新划分区域

　　循环更改上下限重复查找

#include <stdio.h>#include <string.h>#include <stdlib.h>int paixu(int *a);int chazhao(int *a,int b);

int main(){int a[10] = { 2, 56, 58, 685, 459, 32, 1, 52, 68, 45 };paixu(a);int xiabiao = 0;xiabiao = chazhao(a, 685);printf("%d ", xiabiao);return 0;}
int paixu(int *a){int len = sizeof(a);for (int i = 0; i < len; i++){for (int j = 0; j < len - 1; j++){if (a[j] < a[j + 1]){int tmp = a[j];a[j] = a[j + 1];a[j + 1] = tmp;}}}}
int chazhao(int *a, int b)//b为想查找的数据{//下标int xiabiao = 0;//区域下限int low = 0;//区域上限 初次上限取为数组的最大宽度int high = sizeof(a);//二分法取得中间值int middle;
while (high > low){//一开始中间值为数组的中间middle = (low + high) / 2;//判断直到当b等于中间值时 输出中间值的下标if (b == a[middle]){return middle;}//进行循环时 如果b小于中间值 则更改上限，把刚才的中间值变为上限if (b < a[middle]){high = middle-1;}//如果b>中间值，则更改下限if (b >a[middle]){low = middle+1;}}}