实验五

task.1.1

#include<stdio.h>
#define N 4

int main(){
    int x[N] = {1, 9, 8, 4};
    int i;
    int *p;
    
    //方式一：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");
    
    //方式二：通过指针变量遍历输出数组元素（写法一）
    for(p = x; p < x + N; ++p)
    printf("%d", *p);
    printf("\n");
    
    //方式二：通过指针变量遍历输出数组元素（写法二）
    p = x;
    for(i = 0; i < N; ++i)
    printf("%d",*(p + i));
    printf("\n");
    
    //方式二：通过指针变量遍历输出数组元素（写法三）
    p = x;
    for(i = 0; i < N; ++i)
    printf("%d", p[i]);
    printf("\n");
    
    return 0; 
}

task.1.2

#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
    
    //使用数据名、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"); 
    } 
    
    //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;
}

task.2.1

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

int main(){
    char s1[] = "Learning makes me happy";
    char s2[] = "Learning makes me sleep";
    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;
}

问题一：数组s1的大小是23，sizeof(s1)计算的是带\0的长度，strlen则不带
问题二：不能，s1是一个数组不能直接等于
问题三：执行后交换

task.2.2

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

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

问题一：指针变量s1中存放的是字符串的起始地址，sizeof(s1)计算的是指针所占的字节数，strlen(s1)统计的还是数组的长度
问题二：可以，一个是数组，一个是指针所指向的地方被赋予的一串字符
问题三：交换的是指针的指向，实际在储存单元中没有被交换

task.3

#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++)
    ;
}

task.4

#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;
} 

task.5

#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';
}

 

task.6.1

#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;
    }
}

task.6.2

#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, 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;
        }
    }
}

交换的是指针的指向

task.7

#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\tTrue\n", pid[i]);
    else
    printf("%s\tFalse\n",pid[i]);
    
    return 0;                
} 

int check_id(char *str){
    char *p, *j;
    int cnt = 0;
    p = str;
    j = str;
    while(*p){
        cnt++;
        p++;
    }
    if(cnt == 18){
        while(*j){
            if((*j >= 48&&*j <=57)||*j == 88)
            j++;
            else
            return 0;
        }
        return 1;
    }else
    return 0;
}

 

task.8

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

int main(){
    char words[N];
    
    printf("输入英语文本：");
    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){
        if((*s >= 65&&*s<90)||(*s>=97&&*s<122)){
            *s=*s + 1;
        } else if(*s == 90){
            *s = 65;
        }else if(*s == 122){
            *s = 97;
        }
        s++;
    }
}

void decoder(char *s){
    while(*s){
        if((*s > 65&&*s<=90)||(*s>97&&*s<=122)){
            *s = *s - 1;
        }else if(*s == 65){
            *s = 90;
        }else if(*s == 97){
            *s = 122;
        }
        s++;
    }
}