二分查找法C语言实现

【问题描述】

　　生成一个随机数组A[64] ，在数组中查找是否存在某个数num。

【答案】

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

//普通查找：
int Search(int *p, int n, int num)    //找到返回下标，未找到返回-1
{
    for (int i = 0; i < n; i++)
    {
        if (p[i] == num)
            return i;
    }

    return -1;
}

//冒泡排序：
void Sort(int *p, int n)
{
    for (int i = 0; i < n - 1; i++)
    {
        for (int j = 0; j < n - 1 - i; j++)
        {
            if (p[j] > p[j+1])
            {
                int tmp = p[j];
                p[j] = p[j + 1];
                p[j + 1] = tmp;
            }
        }
    }
}

//二分查找：
int BinarySearch(int *p, int n, int num)
{
    int low, high, mid;
    low = 0;
    high = n - 1;
    mid = (low + high) / 2;

    while (low <= high)
    {
        if (num == p[mid])
            return mid;
        else if (num < p[mid])
        {
            high = mid - 1;
            mid = (low + high) / 2;
        }
        else
        {
            low = mid + 1;
            mid = (low + high) / 2;
        }
    }

    return -1;
}

void main()
{
    int a[64];
    time_t tms;
    srand((unsigned int)time(&tms));    //生成随机数种子

    for (int i = 0; i < 64; i++)
    {
        a[i] = rand() % 100;            //0~100之间的随机数
        printf("%d
", a[i]);
    }
    
    //int num;
    //printf("请输入要查找的数：
");
    //scanf("%d", &num);

    int ret;
    //ret = Search(a, 64, num);
    
    Sort(a, 64);

    printf("排序后：
");
    for (int i = 0; i < 64; i++)
        printf("%d
", a[i]);
    int num;
    printf("请输入要查找的数：
");
    scanf("%d", &num);

    ret = BinarySearch(a, 64, num);

    if (ret == -1)
        printf("未找到！
");
    else
        printf("找到a[%d]=%d
",ret,num);

    system("pause");
}