C练习小题

1.每瓶汽水1元，两个空瓶可以置换一瓶汽水，现在有20元，最多能喝多少瓶汽水。

#include <stdio.h>
int main()
{
    int money = 0;
    int total = 0;
    int empty = 0;
    int last = 0;
    scanf("%d", &money);
    total = money;
    empty = money;
    while (empty > 1)
    {
        total += empty / 2;
        empty = empty / 2 + empty % 2;
    }
    printf("%d\n", total);
    system("pause");
    return 0;
}

2.判断一个字符串是否为另外一个字符串旋转之后的字符串
第一种：

#include <stdio.h>
#include <string.h>

int main()
{
    char str1[] = "abcdef";
    char str2[] = "abcdef";
    int len = strlen(str1);
    int i = 0;
    for (i = 0; i < len; i++)
    {
        char tmp = str1[0];
        int k = 0;
        for (k = 0; k < len - 1; k++)
        {
            str1[k] = str1[k + 1];
        }
        str1[len-1] = tmp;
        if (strcmp(str1, str2) == 0)
        {
            printf("是旋转后的字符串\n");
            system("pause");
            return 0;
        }
    }
    printf("不是旋转之后的字符串\n");
    system("pause");
    return 0;
}

第二种：

#include <stdio.h>
#include <assert.h>
#include <string.h>

char *my_strncat(char *dest, const char *src, size_t count)
{
    assert(dest);
    assert(src);
    char *ret = dest;

    while (*dest)
    {
        dest++;
    }
    while (count--)
    {
        *dest++ = *src++;
    }
    return ret;
}


int main()
{
    char str1[20] = "abcdef";
    char str2[] = "cdef";
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    my_strncat(str1, str1, 6);
    if ((len1 == len2) && (NULL != strstr(str1, str2)))
        printf("是旋转\n");
    else
        printf("不是旋转\n");
    system("pause");
    return 0;
}

小知识：

//#include <stdio.h>
//#include <stdlib.h>
//
//int main()
//{
//    int arr[10];
//    printf("arr = %p\n", arr);
//    printf("&arr = %p\n", &arr);
//    int *p = arr;
//    int (*q)[10] = &arr;//&arr得到数组的地址，类型是数组指针
//    printf("p = %p\n", p);
//    printf("q = %p\n", q);
//    printf("p+1 = %p\n", p+1);
//    printf("q+1 = %p\n", q+1);
//    system("pause");
//    return 0;
//}

//
//#include <stdio.h>
//int main()
//{
//    int a[5] = { 1, 2, 3, 4, 5 };
//    int *ptr = (int *)(&a + 1);
//    printf("%d,%d", *(a + 1), *(ptr - 1));
//    system("pause");
//    return 0;
//}

//int main()
//{
//    char*p = "abcdef";
//    char arr[] = "abcdef";
//    printf("%c\n", *(arr + 3));
//    printf("%c\n", arr[3]);//p[3] === *(p+3)
//    system("pause");
//    return 0;
//}

//#include <stdio.h>
//extern int num;
//extern char p[];
//extern void fun();
////extern char *arr;//声明成指针
//int main()
//{
//    printf("%s\n",(char *)(*(int*)p));
//    fun();
//    system("pause");
//    return 0;
//}

#include <stdio.h>

char *pc[10];
int *pi[10];
int(*ppi)[10];
char(*ppc)[10];
int *(*pppi)[10];
char *(*pppc)[10];
int main()
{
    ppc = &pc;
    printf("%d\n", sizeof(pc));//40
    printf("%d\n", sizeof(pi));//40
    printf("%d\n", sizeof(ppi));//4
    printf("%d\n", sizeof(ppc));//4
    printf("%d\n", sizeof(pppi));//4
    printf("%d\n", sizeof(pppc));//4
    printf("%d\n", sizeof(*pc));//4
    printf("%d\n", sizeof(*pi));//4
    printf("%d\n", sizeof(*ppi));//40
    printf("%d\n", sizeof(*pppi));//40
    printf("%d\n", sizeof(*pppc));//40
    system("pause");
    return 0;
}