实验5

task 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");
    
    return 0;
} 

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

#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");
    
    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;
    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;
} 

 

task 2_1

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

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

回答问题：

1、24个字节；sizeof(s1)计算的是数组s1的大小，strlen统计的是字符串的长度

2、不能。因为s1是指针变量，储存地址而非字符串

3、是

 

task 2_2

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

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

回答问题：

1、s1存放的是数组首元素的地址，sizeof(s1)计算的是s1的长度，strlen(s1)统计的是其所包含的字符串的长度。

2、能。task2_1中调用的是指针（地址），task2_2中调用的是数组内容

3、交换的是各自的地址；没有交换。

 

 

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++);
} 

 

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--;
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

#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;
}
}

 

task6_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;
}
}
}

回答问题：

交换的是指针变量的值

 

task7

#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;
    int i;
    
    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>
#include <string.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)
{
    while(*s){
        if(*s >= 'a' && *s <= 'y' || *s >= 'A' && *s <= 'Y'){
            *s += 1;
            s++;
            continue; 
        }
        else if(*s == 'z' || *s == 'Z'){
            *s -= 25;
            s++;
            continue;
        }
        s++;
    }
}

void decoder(char *s)
{
    while(*s){
        if(*s >= 'b' && *s <= 'z' || *s >= 'B' && *s <= 'Z'){
            *s -= 1;
            s++;
            continue;
        }
        else if(*s == 'a' || *s == 'A'){
            *s += 25;
            s++;
            continue;
        }
        s++;
    }


}