c疑难点

Posted 2023-02-25 飞雪天龙

很容易得出p[-2]=10,p[-1]=20,p[0]=30,p[1]=40,p[2]=50,p[3]=60;

p++，指针p往后移一个单位，则p=a+3,此时p[0]=*(p+0)=40;

*p++, 是先取出*p的值，再执行p++操作, 则*p++=40,p=a+4;

*++p,p先往后移一个单位，再取对应地址的值,则*++p=60;

++*p, 则是先取出*p的值，对*p的值再加1，则++*p=61;

int a=0;
int * const p=&a; //指向整型的常指针 指针指向的内容可变，指针的指向不可变（地址不可变）
const int *p=&a; //指向常整型的指针 指针指向可变，指向内容不可变
const int * const *p=&a;//指向常整型的常指针  指针指向内容和指向都不可变

#include
#include
int main()

int a=100, b=200;

const int *p = &a;
int * const q = &b; 
printf("a=%d, *p=%d\\n", a, *p);
printf("b=%d, *q=%d\\n", b, *q);
/* 不可利用*p 间接更改a变量值 
*p=b;
  */
/* 但可以将p指针指向另一变量的地址 */ 
p=&b;
printf("*p=%d\\n", *p);
/*===========================*/

/* 不可更改 q 指针指向另一变量的地址
q=&a;
  */
/* 但可以利用q指针间接更改b变量值 */ 
*q=888;
printf("*q=%d\\n", *q);
 
getch();
return 0;

数组和指针

1.
    int arr[]= 100, 101, 102;
    int *ptr = arr;
    size = (sizeof arr/ sizeof (arr[0]) );
    &arr[0]  ==  arr+0   ==ptr+0  ==100的地址
    *(arr+0) ==arr[0] ==ptr[0] == *(ptr+0) ==100

     
2.
    int k[3][4] = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11;

    &k[1][2] ==      *(k + 1) + 2     =k[1]+2     ==6的地址
      上面的表达式加*号为数值6

    *(k[1] + 2)   == *(  (k[1])  +2  )   == k[1][2]  ==6



3
    char *parr[] = "Department", "of", "Information", "Management";
    *parr[3] ==  **(parr+3)  ==M
    *(parr+2) == Information


4.
    int arr2[3][4] = 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22;
    int *parr[3] = arr2[0], arr2[1], arr2[2];

    *(parr + 1)  ==   parr[1] + 0 ==8的地址

    *(parr[1] + 1) ==10

    

结构体
   
1. 内存地址

/* 声明结构变量 */

struct employee

char id[7]; /* ID号码 */

char name[20]; /* 员工姓名 */

int salary; /* 所得薪资 */

;

/* 定义结构变量，并设定其初始值 */

struct employee manager = "D54321", "Peter", 35000;

/* 定义结构指针变量ptr，将它指向结构变量manager的地址 */

struct employee *ptr = &manager;

/* 输出内存的地址 */ 

&ptr= 18ff1c

ptr=   18ff20

&manager= 18ff20

manager.id = 18ff20

ptr->id  = D54321

(*ptr).id =D54321

2.结构体定义

struct student

char firstname[20];

char *lastname;

int score;

;

struct student st1, *st2;

scanf("%s", st1.firstname);  /* 不可以使用指定运算符 */

st1.lastname="小英";       /* 不可以使用scanf函数来输入 */

st2 = (struct student *)malloc(sizeof(struct student));

scanf("%s", st2->firstname);  /* 不可以使用指定运算符 */

st2->lastname="小明";      /* 不可以使用scanf函数来输入 */

3. 结构体传递地址

#include <stdio.h>

#include <conio.h>

struct student

char name[20];

int score;

char *passdown;

;

void passOrdown(struct student *);

void output(struct student *);

int main()

struct student stu;

printf("请输入姓名: ");

scanf("%s", stu.name);

printf("请输入C语言的分数: ");

scanf("%d", &stu.score);

 

passOrdown(&stu);

output(&stu);  

getch();

return 0;

 

void passOrdown(struct student *p)

if (p->score >= 60)

p->passdown = "PASS";  //调用时使用&传递地址，导致函数中改变变量的值可以返回，在output函数中使用得以输出

else 

p->passdown = "DOWN";   

void output(struct student *q)

int i;

printf("\\n\\n%10s %10s %20s\\n", "Name", "Score", "Pass or Down");  

for(i=1; i<=42; i++)

printf("=");

printf("\\n");

printf("%10s %10d %20s\\n", q->name, q->score, q->passdown); 

结果：

4.结构体数组

struct student stu[3];

  int i;

for(i=0; i<3; i++)

printf("请输入第 #%d 位同学的姓名: ", i+1);

scanf("%s", stu[i].name);

printf("请输入第 #%d 位同学C语言的分数: ", i+1);

scanf("%d", &stu[i].score);

printf("\\n");

passOrdown(stu);

output(stu);

getch();

return 0;

 

void passOrdown(struct student *p)

int i;

for(i=0; i<3; i++)

if (p->score >= 60)

p->passdown = "PASS";

else 

p->passdown = "DOWN";

p++;

例子：

struct student st[]= "John", 90, st+1, 

"Mary", 85, st+2,

"Peter", 92, st ;

void output(struct student *q)

int i;

printf("\\n\\n%10s %10s %20s\\n", "Name", "Score", "Pass or Down");

for(i=1; i<=42; i++)

printf("=");

printf("\\n");

for(i=0; i<3; i++)

printf("%10s %10d %20s\\n", q->name, q->score, q->passdown);

q++;

5.结构体中有结构体

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
int main()

struct node
char *name;
int score;
struct node *next;
;
struct node *p, *q;
p = (struct node *) malloc(sizeof(struct node));
p->name = "Mary";
p->score = 80;
p->next = NULL;
q = (struct node *) malloc(sizeof(struct node));
q->name = "John";
q->score = 90;
q->next = p;
printf("%s %d\\n", q->name, q->score);
printf("%s %d\\n", q->next->name, q->next->score);
getch();
return 0;

6.

    struct student

char *name;

int score;

struct student *next;

;

struct student st[]=  "John", 90, st+1, 

"Mary", 85, st+2,

"Peter", 92, st ;

struct student *ptr[]=st, st+1, st+2;

++(*ptr)->next)->name =peter

 (*ptr)->next->next->name)=peter

双链表

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1. /* doublyListRandom.c */
   
2. /* 双链表的加入与删除: 以分数的高低加以排序 */
   
3. 
   
4. 
   
5. #include <stdio.h>
   
6. #include <stdlib.h>
   
7. #include <string.h>
   
8. #include <conio.h>
   
9. 
   
10. 
    
11. void init_f(void);    /* 初始化链表，建立一空节点为HEAD */
    
12. void insert_f(void);    /* 插入函数 */
    
13. void delete_f(void);    /* 删除函数 */
    
14. void display_f(void);    /* 输出函数 */
    
15. void modify_f(void);    /* 修改函数 */
    
16.  
    
17. struct student
    
18. char name[20];    /* 姓名 */
    
19. int score;    /* 分数 */
    
20. struct student *llink;    /* 节点左链结 */
    
21. struct student *rlink;    /* 节点右链结 */
    
22. ;
    
23. 
    
24. 
    
25. struct student *ptr, *head, *tail, *current_n, *prev;
    
26. 
    
27. 
    
28. int main()
    
29. 
    
30. char option1;
    
31. 
    
32. 
    
33. init_f();
    
34. while(1)
    
35. printf("\\n ****************\\n");
    
36. printf(" 1.insert\\n");
    
37. printf(" 2.delete\\n");
    
38. printf(" 3.display\\n");
    
39. printf(" 4.modify\\n");
    
40. printf(" 5.quit\\n");
    
41. printf(" *******************\\n");
    
42. printf(" Enter your choice (1-5): ");
    
43. option1 = getche();
    
44. switch(option1)
    
45. case '1':
    
46. insert_f();
    
47. break;
    
48. case '2':
    
49. delete_f();
    
50. break;
    
51. case '3':
    
52. display_f();
    
53. break;
    
54. case '4':
    
55. modify_f();
    
56. break;
    
57. case '5':
    
58.      printf("\\n");
    
59. return 0;
    
60. 
    
61. 
    
62. 
    
63. 
    
64. 
    
65. void init_f(void) /* 设一HEAD，将左右链结都指向本身 */
    
66. 
    
67. ptr = (struct student *) malloc(sizeof(struct student));
    
68. strcpy(ptr->name, "0");
    
69. ptr->llink = ptr;
    
70. ptr->rlink = ptr;
    
71. head = ptr;
    
72. tail = ptr;
    
73. 
    
74. 
    
75. 
    
76. /* 根据分数的高低加入 */
    
77. void insert_f(void)
    
78. 
    
79. char s_temp[4];
    
80. 
    
81. 
    
82. ptr = (struct student *) malloc(sizeof(struct student));
    
83. printf("\\n Student name : ");
    
84. gets(ptr->name);
    
85. printf(" Student score: ");
    
86. gets(s_temp);
    
87. ptr->score = atoi(s_temp);
    
88.  
    
89. prev = head;
    
90. current_n = head->rlink;
    
91. while((current_n != head) && (current_n->score >= ptr->score))
    
92. prev = current_n;
    
93. current_n = current_n->rlink;
    
94. 
    
95. ptr->rlink = current_n;
    
96. ptr->llink = prev;
    
97. prev->rlink = ptr;
    
98. current_n->llink = ptr;
    
99. 
    
100. 
     
101. 
     
102. void delete_f(void)
     
103. 
     
104. char del_name[20], ans;
     
105. int count = 0;
     
106. 
     
107. 
     
108. if(head->rlink == head)
     
109. printf("\\n No student record\\n");
     
110. else
     
111. printf("\\n Delete student name: ");
     
112. gets(del_name);
     
113. prev = head;
     
114. current_n = head->rlink;
     
115. while ((current_n != head) && (strcmp(current_n->name,
     
116.                                del_name)!=0))
     
117. prev = current_n;
     
118. current_n = current_n->rlink;
     
119. 
     
120. if (current_n != head)
     
121. /* 确认是否要删除 */
     
122. printf(" Are you sure? ");
     
123. ans=getche();
     
124. if (ans == 'Y' || ans == 'y')
     
125. prev->rlink = current_n->rlink;
     
126. current_n->rlink->llink = prev;
     
127. free(current_n);
     
128. printf("\\n Student %s has been deleted\\n",del_name);
     
129. 
     
130. 
     
131. else
     
132. printf("\\n Student %s not found\\n",del_name);
     
133. 
     
134. 
     
135. 
     
136. 
     
137. void modify_f(void)
     
138. 
     
139. int count = 0;
     
140. char n_temp[20], s_temp[4];
     
141. 
     
142. 
     
143. if(head->rlink == head)
     
144. printf("\\n No student recond\\n"); /* 无数据显示错误 */
     
145. else
     
146. printf("\\n Modify student name: ");
     
147. gets(n_temp);
     
148. current_n=head->rlink;
     
149. while ((current_n != head) && (strcmp(current_n->name , n_temp)!=0))
     
150. prev = current_n;
     
151. current_n = current_n->rlink;
     
152. 
     
153. if (current_n != head)
     
154. printf("\\n **************************\\n");
     
155. printf(" Student name : %s\\n",current_n->name);
     
156. printf(" Student score: %d\\n",current_n->score);
     
157. printf(" **************************\\n");
     
158. printf(" Please enter new score: ");
     
159. gets(s_temp);
     
160. current_n->score = atoi(s_temp);
     
161. printf("\\n %s student record(s) modified\\n", n_temp);
     
162. 
     
163. else // 找不到数据则显示错误
     
164. printf("\\n Student %s not found\\n",n_temp);
     
165. 
     
166. 
     
167. 
     
168. 
     
169. void display_f(void)
     
170. 
     
171. int count = 0;
     
172. 
     
173. 
     
174. if(head->rlink == head)
     
175. printf("\\n No student record\\n");
     
176. else
     
177. printf("\\n\\n NAME SCORE\\n");
     
178. printf(" --------------------\\n");
     
179. current_n = head->rlink;
     
180. while(current_n != head)
     
181. printf(" %-10s %3d\\n", current_n->name,
     
182.        current_n->score);
     
183. count++;
     
184. current_n = current_n->rlink;
     
185. if(count % 20 == 0) getch(); /* 每次输出20条数据 */
     
186. 
     
187. printf(" ---------------------\\n");
     
188. printf(" Total %d record(s) found\\n", count);
     

队列
                                                                                                                                                                                                                                                         

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1. /* queue.c */
   
2. /* 加入在链表的尾节点和删除在头节点 */
   
3. #include <stdio.h>
   
4. #include <conio.h>
   
5. #include <string.h>
   
6. #include <stdlib.h>
   
7. #include <ctype.h>
   
8. void Insert();
   
9. void Delete();
   
10. void Display();
    
11. void Quit();
    
12. struct student
    
13. 
    
14.     int id;
    
15.     int score;
    
16.     struct student *next;
    
17. ;
    
18. struct student *x,*head,*current, *prev;
    
19. 
    
20. int main()
    
21. 
    
22.     /* 链表的第一个节点不存放数据 */
    
23.     head=(struct student *)malloc(sizeof(struct student));
    
24.     head->next= NULL;
    
25.     for(;;)
    
26.     
    
27.         int a;
    
28.         printf("\\n");
    
29.         printf("1)Insert\\n2)Delete\\n3)Display\\n4)Quit\\n");
    
30.         printf("Which one: ");
    
31.         scanf("%d",&a);
    
32.         printf("\\n");
    
33.         switch(a)
    
34.         
    
35.             case 1:Insert();
    
36.                     break;
    
37.             case 2:Delete();
    
38.                     break;
    
39.             case 3:Display();
    
40.                     break;
    
41.             case 4:Quit();
    
42.                     break;
    
43.         
    
44.     
    
45.     printf("\\n\\n~~~~~~~~~~~~~~~FINISH~~~~~~~~~~~~~~~~");
    
46.     getch();
    
47.     return 0;
    
48. 
    
49. 
    
50. /* 加在尾节点 */
    
51. void Insert()
    
52. 
    
53.     x=(struct student *)malloc(sizeof(struct student));
    
54.     printf("Please input your ID: ");
    
55.     scanf("%10d",&x->id);
    
56.     printf("Please input your score: ");
    
57.     scanf("%d",&x->score);
    
58.     x->next=NULL;
    
59.     
    
60.     if(head->next == NULL)
    
61.         head->next = x;
    
62.     else
    
63.     
    
64.         /* 追踪链表的尾节点 */
    
65.         current = head->next;
    
66.         while(current->next != NULL)
    
67.             current = current->next;
    
68.         current->next = x;
    
69.     
    
70.     printf("====================================\\n");
    
71. 
    
72. 
    
73. /* 删除头节点 */
    
74. void Delete()
    
75. 
    
76.     char ch;
    
77. 
    
78.     if(head->next == NULL)
    
79.         printf("The queue is empty!\\n");
    
80.         printf("====================================\\n");
    
81.         return;
    
82.     
    
83.     printf("Are you sure (y/n)? ");
    
84.     ch=getche();
    
85.     /* 确认是否要删除 */
    
86.     if(tolower(ch) == 'y')
    
87.     
    
88.         current = head->next;
    
89.         head->c疑难点

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