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c疑难点

分类： 嵌入式

2016-03-26 01:37:47

指针编程艺术



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

#include


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
#include
#include
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


点击(此处)折叠或打开

  1. /* doublyListRandom.c */
  2. /* 双链表的加入与删除: 以分数的高低加以排序 */


  5. #include <stdio.h>
  6. #include <stdlib.h>
  7. #include <string.h>
  8. #include <conio.h>


  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. };


  25. struct student *ptr, *head, *tail, *current_n, *prev;


  28. int main()
  29. {
  30. char option1;


  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. }


  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. }


  76. /* 根据分数的高低加入 */
  77. void insert_f(void)
  78. {
  79. char s_temp[4];


  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. }


  102. void delete_f(void)
  103. {
  104. char del_name[20], ans;
  105. int count = 0;


  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. }


  137. void modify_f(void)
  138. {
  139. int count = 0;
  140. char n_temp[20], s_temp[4];


  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. }


  169. void display_f(void)
  170. {
  171. int count = 0;


  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);
  189. }


队列
                                                                                                                                                                                                                                                         

点击(此处)折叠或打开

  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;

  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. }

  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. }

  73. /* 删除头节点 */
  74. void Delete()
  75. {
  76.     char ch;

  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->next = current->next;
  90.         printf("\n%d record has been deleted!!!", current->id);
  91.         free(current);
  92.     }
  93.     printf("\n====================================\n");
  94. }

  96. void Display()
  97. {
  98.     if(head->next == NULL)
  99.         printf("The queue is empty!\n");
  100.     else
  101.     {
  102.         /* 将head 指定给currnt，利用current指针将链表的所有节点输出 */
  103.         current=head->next;
  104.         while(current!=NULL)
  105.         {
  106. printf("ID:%d, score=%d\n", current->id,
  107.                               current->score);
  108.             current=current->next;
  109.         }
  110.     }
  111.     printf("====================================\n");
  112. }

  114. void Quit()
  115. {
  116.     exit(0);
  117. }

栈

            

点击(此处)折叠或打开

  1. /* stack.c */
  2. /* 加入和删除都在链表的头节点 */
  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;

  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.     int a;
  27.     printf("\n");
  28.     printf("1)Insert\n2)Delete\n3)Display\n4)Quit\n");
  29.     printf("Which one: ");
  30.     scanf("%d",&a);
  31.     printf("\n");
  32.     switch(a)
  33.     {
  34.     case 1:Insert();
  35.     break;
  36.     case 2:Delete();
  37.     break;
  38.     case 3:Display();
  39.     break;
  40.     case 4:Quit();
  41.     break;
  42.     }
  43.     }
  44.     printf("\n\n~~~~~~~~~~~~~~~FINISH~~~~~~~~~~~~~~~~");
  45.     getch();
  46.     return 0;
  47. }
  48.  
  49. /* 加入一节点于链表头节点 */
  50. void Insert()
  51. {
  52.     /* 分配内存，并指定数据 */
  53.     x=(struct student *)malloc(sizeof(struct student));
  54.     printf("Please input your ID: ");
  55.     scanf("%d",&x->id);
  56.     printf("Please input your score: ");
  57.     scanf("%d",&x->score);
  58.     x->next=NULL;
  59.     
  60.     x->next=head->next;
  61.     head->next=x;
  62.     printf("====================================\n");
  63. }

  65. /* 删除链表头节点的节点 */
  66. void Delete()
  67. {
  68.     char ch;
  69.     /* 判断链表是否有数据 */
  70.     if(head->next == NULL)
  71.     {
  72.     printf("The stack is empty!\n");
  73.     printf("====================================\n");
  74.     return;
  75.     }
  76.     printf("Are you sure (y/n)? ");
  77.     ch=getche();
  78.     
  79.     if(tolower(ch) == 'y')
  80.       {
  81.     current=head->next;
  82.     printf("\n%d record has been deleted!!!", current->id);
  83.     head->next=current->next;
  84.     free(current);
  85.     }
  86.     printf("\n====================================\n");
  87. }

  89. void Display()
  90. {
  91.     if(head->next == NULL)
  92.     printf("The stack is empty!\n");
  93.     else
  94.     {
  95.     current=head->next;
  96.     while(current!=NULL)
  97.     {
  98. printf("ID:%d, score=%d\n",current->id,current->
  99.         score);
  100. current=current->next;
  101.     }
  102.     }
  103.     printf("====================================\n");
  104. }

  106. void Quit()
  107. {
  108.     exit(0);
  109. }


链表

        

点击(此处)折叠或打开

  1. /* singleListRandom.c */
  2. #include <stdio.h>
  3. #include <stdlib.h>
  4. #include <string.h>
  5. #include <conio.h>
  6.  
  7. void insert_func(void);
  8. void sort_func(void);
  9. void delete_func(void);
  10. void display_func(void);
  11. void modify_func(void);
  12. void anykey_func(void);

  14. struct student {
  15.     char name[20];
  16.     int score;
  17.     struct student *next;
  18. };
  19. struct student *ptr, *head, *current, *prev;

  21. int main()
  22. {
  23.     char option1;
  24.     head = (struct student *) malloc(sizeof(struct student));
  25.     head->next=NULL;
  26.     while(1) {
  27.         printf("\n");
  28.         printf("******************\n");
  29.         printf(" 1.insert\n");
  30.         printf(" 2.delete\n");
  31.         printf(" 3.display\n");
  32.         printf(" 4.modify\n");
  33.         printf(" 5.quit\n");
  34.         printf("*******************\n");
  35.         printf(" Enter your choice (1-5): ");
  36.         option1=getche();
  37.         printf("\n");
  38.         switch(option1)    {
  39.             case '1':
  40.                 insert_func();
  41.                 break;
  42.             case '2':
  43.                 delete_func();
  44.                 break;
  45.             case '3':
  46.                 display_func();
  47.                 break;
  48.             case '4':
  49.                 modify_func();
  50.                 break;
  51.             case '5':
  52.                  printf("\n");
  53.                 return 0;
  54.         }
  55.     }
  56. }

  58. /* 加入是以分数的高低加以排序 */
  59. void insert_func(void)
  60. {
  61.     char s_temp[4];
  62.     ptr=(struct student *) malloc(sizeof(struct student));
  63.     printf(" Student name : ");
  64.     gets(ptr->name);
  65.     printf(" Student score: ");
  66.     gets(s_temp);
  67.     ptr->score = atoi(s_temp);
  68.  
  69.     prev = head;
  70.     current = head->next;
  71.     while ((current != NULL) && (current->score > ptr->score)) {
  72.         prev = current;
  73.         current = current->next;
  74.     }
  75.     ptr->next = current;
  76.     prev->next = ptr;
  77. }

  79. /* 删除是以姓名为键值*/
  80. void delete_func(void)
  81. {
  82.     char del_name[20], ans;
  83.     printf(" Delete student name: ");
  84.     gets(del_name);
  85.     
  86.     prev = head;
  87.     current = head->next;
  88. while ((current != NULL) && (strcmp(current->name ,
  89.         del_name)!=0)) {
  90.         prev = current;
  91.         current = current->next;
  92.     }
  93.     if (current != NULL) {
  94.         /* 确认是否要删除 */
  95.         printf(" Are you sure? ");
  96.         ans=getche();
  97.         if (ans == 'Y' || ans == 'y') {
  98.             prev->next = current->next;
  99.             free(current);
  100.             printf(" Student %s has been deleted\n", del_name);
  101.         }
  102.     }
  103.     else
  104.         printf(" Student %s not found\n",del_name);
  105.  }

  107. void modify_func(void)
  108. {
  109.     char n_temp[20],s_temp[4];
  110.     printf(" Modify student name: ");
  111.     gets(n_temp);
  112.     current=head->next;

  114. while ((current != NULL) && (strcmp(current->name , n_temp)!=0)) {        
  115. prev = current;
  116.      current = current->next;
  117.     }
  118.     if (current != NULL) {
  119.         printf(" **************************\n");
  120.         printf(" Student name : %s\n",current->name);
  121.         printf(" Student score: %d\n",current->score);
  122.         printf(" **************************\n");
  123.         printf(" Please enter new score: ");
  124.         gets(s_temp);
  125.         current->score = atoi(s_temp);
  126.         printf(" Student %s has been modified\n",n_temp);
  127.     }
  128.     else
  129.         printf(" Student %s not found\n",n_temp);
  130. }

  132. void display_func(void)
  133. {
  134.     int count=0;

  136.     if(head->next == NULL) {
  137.         printf(" No student record\n");
  138.     }
  139.     else {
  140.         printf("\n");
  141.         printf(" NAME SCORE\n");
  142.         printf(" ----------------\n");
  143.         current=head->next;
  144.         while(current != NULL) {
  145. printf(" %-10s %3d\n", current->name,
  146.         current->score);
  147.             count++;
  148.             current=current->next;
  149.             if(count % 20 == 0) getch();
  150.         }
  151.         printf(" ----------------\n");
  152.         printf(" Total %d record(s) found\n", count);
  153.     }
  154. }




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