实验5 指针

task1.1

#include<stdio.h>
#define N 4

int main()
{
    int x[N] = {1,9,8,4};
    int i;
    int *p;
    
    //通过数组名和下标遍历输出数组元素
    for(i=0;i<N;i++)
        printf("%d",x[i]);
    printf("\n");
    
    //通过指针变量遍历输出数组元素(写法1)
    for(p=x;p<x+N;++p)
        printf("%d",*p);
    printf("\n");
    
    
    //通过指针变量遍历输出数组元素（写法2）
    p=x;
    for(i=0;i<N;++i)
        printf("%d",*(p+i));
    printf("\n");
     
    //通过指针变量遍历输出数组元素（写法3） 
    p=x;
    for(i=0;i<N;++i)
        printf("%d",p[i]);
    printf("\n");
    
    return 0; 
 }

task1.2

#include<stdio.h>

int main()
{
    int x[2][4] = {{1,9,8,4},{2,0,4,9}};
    int i,j;
    int *p;    //指针变量，存放int类型数据的地址 
    int(*q)[4];    //指针变量，指向包含4个int型元素的一维数组
    
    //使用数组名、下标访问二维数组元素
    for(i=0;i<2;++i)
    {
        for(j=0;j<4;++j)
            printf("%d",x[i][j]);
        printf("\n");    //输出完一行换行 
    }
    
    //使用指针变量p间接访问二维数组元素
    for(p=&x[0][0],i=0; p<&x[0][0]+8; ++p,++i)
    {
        printf("%d",*p);
        if((i+1)%4==0)
        printf("\n");
    }
    
    //使用指针变量q间接访问二维数组元素
    for(q=x; q<x+2; ++q)
    {
        for(j=0; j<4; ++j)
            printf("%d",*(*q+j));
        printf("\n");
     } 
     
     return 0;
}

task2.1

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

int main()
{
    char s1[] = "Learning makes me happy";
    char s2[] = "Learning makes me sleepy";
    char tmp[N];
    
    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");
    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：s1数组大小是24，sizeof(s1)计算的是占用的字节数，strlen(s1)统计的是有效字符数，即除空字符以外的字符个数

问题2：不能，定义的是字符型的数组，因此要带方括号

问题3：s1与s2发生交换了

task2.2

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

int main()
{
    char *s1 = "Learning makes me happy";
    char *s2 = "Learning makes me sleepy";
    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);
}

问题1：指针变量里存放的是字符串的起始地址，sizeof(s1)计算的是第一个单词的长度，strlen(s1)统计的是整个字符串的有效字符数（包括空格）

问题2：可以替换，

问题3：交换的是指针，两个字符串常量没有发生交换

task3

#include<stdio.h>

void str_cpy(char *target,const char *source);
void str_cat(char *str1,char *str2);

int main()
{
    char s1[80],s2[20] = "1984";
    
    str_cpy(s1,s2);
    puts(s1);
    
    str_cat(s1,"Animal Farm");
    puts(s1);
    
    return 0;
}

void str_cpy(char *target,const char *source)
{
    while (*target++=*source++);
}

void str_cat(char *str1,char *str2)
{
    while (*str1)
        str1++;
        
    while (*str1++=*str2++);
}

task4

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

int main()
{
    char str[80];
    
    while(gets(str)!=NULL)
    {
        if(func(str))
            printf("yes\n");
        else
            printf("no\n");
    }
    return 0;
}

int func(char *str)
{
    char *begin,*end;
    begin = end = str;
    while(*end)
        end++;
        
    end--;
    
    while(begin<end)
    {
        if(*begin!=*end)
            return 0;
        else
        {
            begin++;
            end--;
        }
    }
    
    return 1;
}

task5

#include<stdio.h>
#define N 80

void func(char *);

int main()
{
    char s[N];
    
    while(scanf("%s",s)!=EOF)
    {
        func(s);
        puts(s);
    }
    return 0;
}

void func(char *str)
{
    int i;
    char *p1,*p2,*p;
    
    p1 = str;
    while(*p1=='*')
        p1++;
    p2 = str;
    while(*p2)
        p2++;
    p2--;
    
    p = str;
    i=0;
    while(p<p1)
    {
        str[i] = *p;
        p++;
        i++;
    }
    while(p<=p2)
    {
        if(*p!='*')
        {
            str[i] = *p;
            i++;
        }
        p++;
    }
    while(*p!='\0')
    {
        str[i] = *p;
        p++;
        i++;
    }
    str[i] = '\0';
}

task6.1

#include<stdio.h>
#include<string.h>
void sort(char *name[],int n);
int main()
{
    char *course[4] = {"C Program","C++ Object Oriented Program","Operating System","Data Structure and Algorithms"};
    
    int i;
    
    sort(course,4);
    
    for(i=0;i<4;i++)
        printf("%s\n",course[i]);
        
    return 0;
}

void sort(char *name[],int n)
{
    int i,j;
    char *tmp;
    
    for(i=0;i<n-1;++i)
        for(j=0;j<n-1-i;++j)
            if(strcmp(name[j],name[j+1])>0)
            {
                tmp = name[j];
                name[j] = name[j+1];
                name[j+1] = tmp;
            }
}

交换的是指针

task6.2

#include<stdio.h>
void sort(char *name[],int n);

int main()
{
    char *course[4] = {"C Program","C++ Object Oriented Program","Operating System","Data Structure and Algorithms"};
    
    int i;
    sort(course,4);
    for(i=0;i<4;i++)
        printf("%s\n",course[i]);
        
        return 0;
}

void sort(char *name[],int n)
{
    int i,j,k;
    char *tmp;
    
    for(i=0;i<n-1;i++)
    {
        k=i;
        for(j=i+1;j<n;j++)
            if(strcmp(name[j],name[k])<0)
            k=j;
            
        if(k!=i)
        {
            tmp = name[i];
            name[i] = name[k];
            name[k] = tmp;
        }
    }
}

内存中字符串的存储位置发生了交换

task7

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

int check_id(char *str);   //函数声明

int main()
{
    char *pid[N] = {"31010120000721656X","330106199609203301","53010220051126571","510104199211197977","53010220051126133Y"};
    
    int i;
    
    for(i=0;i<N;++i)
        if(check_id(pid[i]))//函数调用
            printf("%s\tTrue\n",pid[i]);
        else
            printf("%s\tFalse\n",pid[i]); 
            
    return 0;
}
 int check_id(char *str)
{
     char *p;
     p = str;
     
     while((*p >= '0' && *p <= '9')||*p=='X')
            p++;
 
    if(*p == '\0' && strlen(str) == 18)
        return 1;
    else
        return 0;
}

task8

#include<stdio.h>
#define N 80
void encoder(char *s);    //函数声明
void decoder(char *s);    //函数声明
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)
{
    while(*s!='\0') 
        {
        if(*s >= 65 && *s <= 90|| *s >= 97&& *s <= 122)
        {
            *s = *s + 1;
            s++; 
            continue;
        }
        else if(*s == 'z'|| *s == 'Z')
        {
            *s = *s - 25;
            s++; 
            continue;
        }
        s++;
    }
}

void decoder(char *s)
{
     while(*s) 
        {
        if(*s >= 66 && *s <= 90 || *s >= 98 && *s <= 122)
        {
            *s = *s - 1;
            s++;
            continue;
        }
        else if(*s == 'A'|| *s == 'a')
        {
            *s = *s + 25;
            s++;
            continue;
        }
        s++;
    }
}

posted @ 2023-05-06 15:20 傲芙阅读(36) 评论(0) 收藏举报

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实验5 指针

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