C语言进阶21收尾(编程练习)(atoi,strncpy,strncat,offsetof模拟实现+找单身狗+宏交换二进制奇偶位）（下）

 
#include<stdio.h>
#include<string.h>
int find_dog(int arr[],int sz)
{
    int dog = 0;
    for (int i = 0;i < sz;i++)
    {
        dog ^= arr[i];
    }
    return dog;
}
int main()
{
    int arr[] = { 1,2,2,3,3,4,1 };
    int sz = sizeof(arr) / sizeof(arr[0]);
    printf("单身狗是%d", find_dog(arr,sz));
    return 0;
}

 
#include<stdio.h>
void find_two_dog(int arr[],int sz,int* px,int* py)
{
    int sum = 0;
    for (int i = 0; i < sz; i++)
    {
        sum ^= arr[i];
    }
    int count = 0;
    for (int i = 0; i < 32; i++)
    {
        if (sum & 1 << i) //循环判断第几位是1
        {
            count = i;//如果是1 记录下来
            break;
        }
    }
    int dog1 = 0, dog2 = 0;
    for (int i = 0; i < sz; i++)
    {
        if (arr[i] & 1 << count)
        {
            dog1 ^= arr[i];
        }
        else
        {
            dog2 ^= arr[i];
        }
    }
    *px = dog1;
    *py = dog2;
}
int main()
{
    int arr[] = { 1,2,3,3,1,4 };
    int sz = sizeof(arr) / sizeof(arr[0]);
    int x = 0, y = 0;//因为不能return两个值，所以设置两个返回型参数
    find_two_dog(arr, sz, &x, &y);
    printf("第一个单身狗%d\n第二个单身狗%d",x, y);
    return 0;
}

 
#include<stdio.h>      //a  1010                   5  0101
#define SWAP(R) (((R) & 0xaaaaaaaa)>>1) + (((R) & 0x55555555)<<1)
int main()
{
    int a = 10;
    printf("%d\n", SWAP(a));
    return 0;
}

 
#include <stdio.h>
#include <stddef.h>
struct S
{
    int a;//0 1 2 3
    char b;//4
    //5
    short c;//6  7
};
int main()
{
    printf("%d\n", offsetof(struct S, a));
    printf("%d\n", offsetof(struct S, b));
    printf("%d\n", offsetof(struct S, c));
    return 0;
}

 
#include <stdio.h>
#include <stddef.h>
//结构体起始地址加上该成员相对于起始地址的偏移量就是成员变量的地址。
//想要知道成员相对于结构体起始地址的偏移量，假设结构体起始地址位于0地址处，
//那么结构体成员变量的地址强制类型转换为size_t后就相当于该成员相对于起始地址的偏移量
#define OFFSETOF(type, member) (size_t)(&(((type*)0)->member))//-0忽略了
struct S 
{
    int a;//0 1 2 3
    char b;//4
    //5
    short c;//6  7
};
int main() 
{
    printf("%d\n", offsetof(struct S, a));
    printf("%d\n", offsetof(struct S, b));
    printf("%d\n", offsetof(struct S, c));
 
    printf("%d\n", OFFSETOF(struct S, a));
    printf("%d\n", OFFSETOF(struct S, b));
    printf("%d\n", OFFSETOF(struct S, c));
    return 0;
}