实验六

1-1

#include<stdio.h>
#define N 4

int main()
{
    int x[N] = { 1,9,8,4 };
    int i;
    int* p;
    for (i = 0; i < N; ++i)
        printf("%d", x[i]);
    printf("\n");

    for (p = x; p < x + N; ++p)
        printf("%d", *p);
    printf("\n");

    p = x;
    for (i = 0; i < N; ++i)
        printf("%d", *(p+i));
    printf("\n");

    p = x;
    for (i = 0; i < N; ++i)
        printf("%d", p[i]);
    printf("\n");

    return 0;
}

2004

1-2

#include<stdio.h>
#define N 4

int main()
{
    char x[N] = { '1','9','8','4' };
    int i;
    char* p;
    
    for (i = 0; i < N; ++i)
        printf("%c", x[i]);
    printf("\n");

    for (p = x; p < x + N; ++p)
        printf("%c", *p);
    printf("\n");

    p = x;
    for (i = 0; i < N; ++i)
        printf("%c", *(p + i));
    printf("\n");

    p = x;
    for (i = 0; i < N; ++i)
        printf("%c", p[i]);
    printf("\n");;

    return 0;
}

2001

因为数组类型不同，第一个是整型数组，第二个是字符型数组，导致指针变量存放的数据类型的地址不同

2-1

#include<stdio.h>

int main()
{
    int x[2][4] = { {1,9,8,4},{2,0,2,2} };
    int i, j;
    int* p;
    int(*q)[4];

    for (i = 0; i < 2; ++i)
    {
        for (j = 0; j < 4; ++j)
            printf("%d", x[i][j]);
        printf("\n");
    }

    for (p = &x[0][0], i = 0; p < &x[0][0] + 8; ++p, ++i)
    {
        printf("%d", *p);
        if ((i + 1) % 4 == 0)
            printf("\n");
    }

    for (q = x; q < x + 2; ++q)
    {
        for (j = 0; j < 4; ++j)
            printf("%d", *(*q + j));
        printf("\n");
    }
    return 0;
}

假设指针变量p初始值是地址2000，则执行++p后，指针变量p中存放的地址值是2004

假设指针变量q初始值是地址2000，则执行++q后，指针变量p中存放的地址值是2016

2-2

#include<stdio.h>

int main()
{
    char x[2][4] = { {'1','9','8','4'},{'2','0','2','2'} };
    int i, j;
    char* p;
    char(*q)[4];

    for (i = 0; i < 2; ++i)
    {
        for (j = 0; j < 4; ++j)
            printf("%c", x[i][j]);
        printf("\n");
    }

    for (p = &x[0][0], i = 0; p < &x[0][0] + 8; ++p, ++i)
    {
        printf("%d", *p);
        if ((i + 1) % 4 == 0)
            printf("\n");
    }

    for (q = x; q < x + 2; ++q)
    {
        for (j = 0; j < 4; ++j)
            printf("%d", *(*q + j));
        printf("\n");
    }

    return 0;
}

2001

2004

指针指向的数组类型不同，sizeof（）算出来所占用字节数不同

3-1

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#define N 80

int main()
{
    char s1[] = "c,i love u.";
    char s2[] = "c,i hate u.";
    char tmp[N];

    printf("sizeof(s1)vs.strlen(s1):\n");
    printf("sizeof(s1)=%d\n", sizeof(s1));
    printf("sizeof(s2)=%d\n", strlen(s1));

    printf("\nbefore swap:\n");
    printf("s1:%s\n", s1);
    printf("s2:%s\n", s2);
    
    printf("\nswapping...\n");    
    strcpy(tmp, s1);
    strcpy(s1, s2);
    strcpy(s2, tmp);

    printf("\nafter swap:\n");
    printf("s1:%s\n", s1);
    printf("s2:%s\n", s2);

    return 0;
}

问题1：数组s1的大小是12，sizeof（s1）计算的是s1的大小，strlen（s1）统计的是s1的有效字符数（除空字符以外的字符个数）

问题2：不能替换

问题3：是的，交换了

3-2

#include<stdio.h>
#include<string.h>
#define N 80

int main()
{
    char* s1;
    s1= "c,i love u.";
    char* s2 = "c,i hate u.";

    char* tmp;

    printf("sizeof(s1)vs.strlen(s1):\n");
    printf("sizeof(s1)=%d\n", sizeof(s1));
    printf("strlen(s1)=%d\n", strlen(s1));

    printf("\nbefore swap:\n");
    printf("s1:%s\n", s1);
    printf("s2:%s\n", s2);

    printf("\nswapping...\n");
    tmp = s1;
    s1 = s2;
    s2 = tmp;

    printf("\nafter swap:\n");
    printf("s1:%s\n", s1);
    printf("s2:%s\n", s2);

    return 0;
}

 

问题1：指针变量s1中存放的是指向字符串常量的字符指针，sizeof（s1）计算的系统给s1分配的内存大小，strlen（s1）统计的是字符串的长度，直到‘\0’为止

问题2：可以换。指针是变量，相当于把字符串的地址交给指针，而3-1中的数组不能，因为数组是常量

问题3：交换的是存放字符串的地址；交换了。

4

 

#include<stdio.h>
#include<string.h>
#define N 5

int check_id(char* str);

int main()
{
    char* pid[N] = { "31010120000721656X",
"330106199609203301",
"53010220051126571",
"510104199211197977",
"53010220051126133Y" };
    int i;

    for (i = 0; i < N; ++i)
        if (check_id(pid[i]))
            printf("%s\tTure\n", pid[i]);
        else
            printf("%s\tFalse\n", pid[i]);

    return 0;
}

int check_id(char* str)
{
    if (strlen(str) != 18)
        return 0;
    int i;
    for (i = 0; i < 18; i++)
    {
        if (str[i] == 'X'||str[i] >= '0' && str[i] <= '9')
            return 1;
        else
            return 0;
    }return 1;
}

5

#include<stdio.h>
#include<string.h>
#define N 80
int is_palindrome(char* s);

int main()
{
    char str[N];
    int flag;

    printf("Enter a string:\n");
    gets(str);

    flag = is_palindrome(str);

    if (flag)
        printf("YES\n");
    else
        printf("NO\n");
}

int is_palindrome(char* s)
{
    int cd,i,md;
    cd = strlen(s);

        md = cd / 2;

        for (i = 0; i < md; i++)
        {
            if (s[i] == s[cd - i-1])
                continue;

            else return 0;
        }
        return 1;
    
}

6

 

#include<stdio.h>
#define N 80
void encoder(char* s);
void decoder(char* s);

int main()
{
    char words[N];
    printf("输入英文文本：");
        gets(words);

        printf("编码后的英文文本：");
        encoder(words);
    printf("%s\n", words);

    printf("对编码后的英文文本解码：");
    decoder(words);
    printf("%s\n", words);

    return 0;
}

void encoder(char* s)
{
    int i;
    for (i = 0; i < N; i++)
    {
        if (s[i] >= 'a' && s[i] < 'z'||s[i] >= 'A' && s[i] <='Z')
            s[i] = s[i] + 1;
        else if (s[i] =='z' || s[i] == 'Z')
            s[i] = s[i] -25;
    }
}

void decoder(char* s)
{
    int i;
    for (i = 0; i < N; i++)
    {
        if (s[i] > 'a' && s[i] <= 'z' || s[i] > 'A' && s[i] <= 'Z')
            s[i] = s[i] - 1;
        else if (s[i] == 'a' || s[i] == 'A')
            s[i] = s[i] +25;
    }

}