实验五

task1_1.c

#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;
 } 

 

task1_2.c

#include <stdio.h>


int main()
{
    int x[2][4] = {{1, 9, 8, 4},{2, 0, 4, 9}};
    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; 

 } 

 task2_1.c

#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：数组s1的大小是24；sizeof(s1)计算的是数组s1的大小，strlen(s1)统计的是除结束符外数组所占的空间。
问题2：不能，因为char s1[ ]定义时未标明字符串长度，违反语法规则。

问题3：line20-22执行后，字符数组s1和s2中的内容交换。
tas2_2.c

#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);
    
    return 0;
 } 

 问题1：

问题2：

问题3：

task3.c

#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.c

#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.c

#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--;
    
    while(*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.c

#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+i]>0))
       {
           tmp = name[j];
           name[j] = name[j+1];
           name[j+1]=tmp;
       }
}

 task6_2.c

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

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

答：实现的是指针变量的值。

task7.c

#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])) // 函数调用
            printf("%s\tTrue\n", pid[i]);
        else
            printf("%s\tFalse\n", pid[i]);

    return 0;
}


int check_id(char *str)
{
    int flag=1;
    char *p=str;
    for(p=str;*p!='\0';p++)
    {
        flag=1;
        if(str[17]!='X'&&(*p<48||*p>57))
            flag=0;
    }
    if(flag==1&&strlen(str)==18) 
        return 1;
    else 
        return 0;
}

 task8.c

#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); // 函数调用
    printf("%s\n", words);

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

    return 0;
}

void encoder(char *s)
{
    for(;*s!='\0';s++)
        if(*s!='z'&&*s!='Z'&&(*s>=65&&*s<=90||*s>=97&&*s<=122))
            *s+=1;
        else if(*s=='z'||*s=='Z')
            *s-=25;
            
}


void decoder(char *s)
{
    for(;*s!='\0';s++)
        if(*s!='a'&&*s!='A'&&(*s>=65&&*s<=90||*s>=97&&*s<=122))
             *s-=1;
        else if(*s=='a'||*s=='A')
            *s+=25;
}