实验五

task1：
`#include <stdio.h>

define N 5

void input(int x[], int n);
void output(int x[], int n);
void find_min_max(int x[], int n, int *pmin, int *pmax);

int main() {
int a[N];
int min, max;

printf("录入%d个数据:\n", N);
input(a, N);

printf("数据是: \n");
output(a, N);

printf("数据处理...\n");
find_min_max(a, N, &min, &max);

printf("输出结果:\n");
printf("min = %d, max = %d\n", min, max);

return 0;

}

void input(int x[], int n) {
int i;

for(i = 0; i < n; ++i)
    scanf("%d", &x[i]);

}

void output(int x[], int n) {
int i;

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

}

void find_min_max(int x[], int n, int *pmin, int *pmax) {
int i;

*pmin = *pmax = x[0];

for(i = 0; i < n; ++i)
    if(x[i] < *pmin)
        *pmin = x[i];
    else if(x[i] > *pmax)
        *pmax = x[i];

}`

1.函数功能是找到五个数中的最大值和最小值并返回

2.都指向x【0】的地址

task2:
`#include <stdio.h>

define N 5

void input(int x[], int n);
void output(int x[], int n);
int *find_max(int x[], int n);

int main() {
int a[N];
int *pmax;

printf("录入%d个数据:\n", N);
input(a, N);

printf("数据是: \n");
output(a, N);

printf("数据处理...\n");
pmax = find_max(a, N);

printf("输出结果:\n");
printf("max = %d\n", *pmax);

return 0;

}

void input(int x[], int n) {
int i;

for(i = 0; i < n; ++i)
    scanf("%d", &x[i]);

}

void output(int x[], int n) {
int i;

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

}

int *find_max(int x[], int n) {
int max_index = 0;
int i;

for(i = 0; i < n; ++i)
    if(x[i] > x[max_index])
        max_index = i;

return &x[max_index];

}`

1.找到五个数中的最大值
2.可以

`#include <stdio.h>

include <string.h>

define N 80

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

}`
1.大小是23 sizeof统计的是字符串的所占字节数，strlrn统计的是字符个数
2.不可以，因为地址已经固定了
3.是

task3:
`#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;

}`
1.s1存放的是这个数组的地址，sizeof计算的是这个地址的字节数，strlen统计的是这个数组的字符数
2.能。1是先定义数组，不能后赋值，2是定义了一个指针，指针指向这个数组内容，所以可以
3.交换的是s1和s2的地址，两个字符串在内存中没有交换

task4:
`#include <stdio.h>

int main() {
int x[2][4] = {{1, 9, 8, 4}, {2, 0, 4, 9}};
int i, j;
int ptr1; // 指针变量，存放int类型数据的地址
int(ptr2)[4]; // 指针变量，指向包含4个int元素的一维数组

printf("输出1: 使用数组名、下标直接访问二维数组元素\n");
for (i = 0; i < 2; ++i) {
    for (j = 0; j < 4; ++j)
        printf("%d ", x[i][j]);
    printf("\n");
}

printf("\n输出2: 使用指针变量ptr1(指向元素)间接访问\n");
for (ptr1 = &x[0][0], i = 0; ptr1 < &x[0][0] + 8; ++ptr1, ++i) {
    printf("%d ", *ptr1);

    if ((i + 1) % 4 == 0)
        printf("\n");
}
                     
printf("\n输出3: 使用指针变量ptr2(指向一维数组)间接访问\n");
for (ptr2 = x; ptr2 < x + 2; ++ptr2) {
    for (j = 0; j < 4; ++j)
        printf("%d ", *(*ptr2 + j));
    printf("\n");
}

return 0;

}`
1.第一个ptr表示指向这个包含四个元素的数组，第二个ptr表示这个数组里有4个指针

task5:
`#include <stdio.h>

define N 80

void replace(char *str, char old_char, char new_char); // 函数声明

int main() {
char text[N] = "Programming is difficult or not, it is a question.";

printf("原始文本: \n");
printf("%s\n", text);

replace(text, 'i', '*'); // 函数调用 注意字符形参写法，单引号不能少

printf("处理后文本: \n");
printf("%s\n", text);

return 0;

}

// 函数定义
void replace(char *str, char old_char, char new_char) {
int i;

while(*str) {
    if(*str == old_char)
        *str = new_char;
    str++;
}

}`
1.把所有的i换成*
2.可以

`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

define N 80

char* str_trunc(char* str, char x);

int main() {
char str[N];
char ch;
while (printf("输入字符串: "), fgets(str)!= NULL) {
printf("输入一个字符: ");
ch = getchar();
printf("截断处理...\n");
str_trunc(str, ch); // 函数调用
printf("截断处理后的字符串: %s\n", str);
getchar(); // 吸收换行符
}
return 0;
}

char* str_trunc(char* str, char x) {
char* p = str;
while (p != '\0') {
if (p == x) {
*p = '\0';
break;
}
p++;
}
return str;
}`

作用是清除上一轮输入的字符串

task6:
`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

include <string.h>

define N 5

int check_id(char* str);

int main()
{
char* pid[N] = { "31010120000721656X",
"3301061996X0203301",
"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) {
int len = strlen(str);
if (len != 18) {
return 0;
}
int i;
for (i = 0; i < len - 1; i++) {
if (!(str[i] >= '0' && str[i] <= '9')) {
return 0;
}
}
if (str[len - 1] != 'X' && !(str[len - 1] >= '0' && str[len - 1] <= '9')) {
return 0;
}
return 1;
}`

task7：
`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

define N 80

void encoder(char* str, int n);
void decoder(char* str, int n);

int main() {
char words[N];
int n;

printf("输入英文文本: ");
fgets(words);

printf("输入n: ");
scanf("%d", &n);

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

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

return 0;

}

void encoder(char* str, int n) {
while (str != '\0') {
if ((str >= 'a' && str <= 'z')) {
str = (str - 'a' + n) % 26 + 'a';
}
else if ((str >= 'A' && *str <= 'Z')) {
str = (str - 'A' + n) % 26 + 'A';
}
str++;
}
}

void decoder(char* str, int n) {
while (str != '\0') {
if ((str >= 'a' && str <= 'z')) {
str = (str - 'a' - n + 26) % 26 + 'a';
}
else if ((str >= 'A' && *str <= 'Z')) {
str = (str - 'A' - n + 26) % 26 + 'A';
}
str++;
}
}`

task8：
`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

include <string.h>

void swap(char** a, char** b) {
char* temp = *a;
*a = *b;
*b = temp;
}

void bubbleSort(char* arr[], int n) {
int i, j;
for (i = 0; i < n - 1; i++) {
for (j = 0; j < n - i - 1; j++) {
if (strcmp(arr[j], arr[j + 1]) > 0) {
swap(&arr[j], &arr[j + 1]);
}
}
}
}

int main(int argc, char* argv[]) {
int i;
if (argc > 1)
bubbleSort(&argv[1], argc - 1);
for (i = 1; i < argc; i++) {
printf("hello, %s\n", argv[i]);
}
}
return 0;
}`