c疑难点

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


 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <conio.h>


 void init_f(void);    /* 初始化链表，建立一空节点为HEAD */
 void insert_f(void);    /* 插入函数 */
 void delete_f(void);    /* 删除函数 */
 void display_f(void);    /* 输出函数 */
 void modify_f(void);    /* 修改函数 */

 struct student {
 char name[20];    /* 姓名 */
 int score;    /* 分数 */
 struct student *llink;    /* 节点左链结 */
 struct student *rlink;    /* 节点右链结 */
 };


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


 int main()
 {
 char option1;


 init_f();
 while(1){
 printf("\n ****************\n");
 printf(" 1.insert\n");
 printf(" 2.delete\n");
 printf(" 3.display\n");
 printf(" 4.modify\n");
 printf(" 5.quit\n");
 printf(" *******************\n");
 printf(" Enter your choice (1-5): ");
 option1 = getche();
 switch(option1){
 case '1':
 insert_f();
 break;
 case '2':
 delete_f();
 break;
 case '3':
 display_f();
 break;
 case '4':
 modify_f();
 break;
 case '5':
      printf("\n");
 return 0;
 }
 }
 }


 void init_f(void) /* 设一HEAD，将左右链结都指向本身 */
 {
 ptr = (struct student *) malloc(sizeof(struct student));
 strcpy(ptr->name, "0");
 ptr->llink = ptr;
 ptr->rlink = ptr;
 head = ptr;
 tail = ptr;
 }


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


 ptr = (struct student *) malloc(sizeof(struct student));
 printf("\n Student name : ");
 gets(ptr->name);
 printf(" Student score: ");
 gets(s_temp);
 ptr->score = atoi(s_temp);

 prev = head;
 current_n = head->rlink;
 while((current_n != head) && (current_n->score >= ptr->score)) {
 prev = current_n;
 current_n = current_n->rlink;
 }
 ptr->rlink = current_n;
 ptr->llink = prev;
 prev->rlink = ptr;
 current_n->llink = ptr;
 }


 void delete_f(void)
 {
 char del_name[20], ans;
 int count = 0;


 if(head->rlink == head)
 printf("\n No student record\n");
 else {
 printf("\n Delete student name: ");
 gets(del_name);
 prev = head;
 current_n = head->rlink;
 while ((current_n != head) && (strcmp(current_n->name,
                                del_name)!=0)) {
 prev = current_n;
 current_n = current_n->rlink;
 }
 if (current_n != head) {
 /* 确认是否要删除 */
 printf(" Are you sure? ");
 ans=getche();
 if (ans == 'Y' || ans == 'y') {
 prev->rlink = current_n->rlink;
 current_n->rlink->llink = prev;
 free(current_n);
 printf("\n Student %s has been deleted\n",del_name);
 }
 }
 else
 printf("\n Student %s not found\n",del_name);
 }
 }


 void modify_f(void)
 {
 int count = 0;
 char n_temp[20], s_temp[4];


 if(head->rlink == head)
 printf("\n No student recond\n"); /* 无数据显示错误 */
 else {
 printf("\n Modify student name: ");
 gets(n_temp);
 current_n=head->rlink;
 while ((current_n != head) && (strcmp(current_n->name , n_temp)!=0)){
 prev = current_n;
 current_n = current_n->rlink;
 }
 if (current_n != head) {
 printf("\n **************************\n");
 printf(" Student name : %s\n",current_n->name);
 printf(" Student score: %d\n",current_n->score);
 printf(" **************************\n");
 printf(" Please enter new score: ");
 gets(s_temp);
 current_n->score = atoi(s_temp);
 printf("\n %s student record(s) modified\n", n_temp);
 }
 else // 找不到数据则显示错误
 printf("\n Student %s not found\n",n_temp);
 }
 }


 void display_f(void)
 {
 int count = 0;


 if(head->rlink == head)
 printf("\n No student record\n");
 else {
 printf("\n\n NAME SCORE\n");
 printf(" --------------------\n");
 current_n = head->rlink;
 while(current_n != head) {
 printf(" %-10s %3d\n", current_n->name,
        current_n->score);
 count++;
 current_n = current_n->rlink;
 if(count % 20 == 0) getch(); /* 每次输出20条数据 */
 }
 printf(" ---------------------\n");
 printf(" Total %d record(s) found\n", count);
 }

队列

                                                                                                                                                                                                                                                         

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 /* queue.c */
 /* 加入在链表的尾节点和删除在头节点 */
 #include <stdio.h>
 #include <conio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
 void Insert();
 void Delete();
 void Display();
 void Quit();
 struct student
 {
     int id;
     int score;
     struct student *next;
 };
 struct student *x,*head,*current, *prev;

 int main()
 {
     /* 链表的第一个节点不存放数据 */
     head=(struct student *)malloc(sizeof(struct student));
     head->next= NULL;
     for(;;)
     {
         int a;
         printf("\n");
         printf("1)Insert\n2)Delete\n3)Display\n4)Quit\n");
         printf("Which one: ");
         scanf("%d",&a);
         printf("\n");
         switch(a)
         {
             case 1:Insert();
                     break;
             case 2:Delete();
                     break;
             case 3:Display();
                     break;
             case 4:Quit();
                     break;
         }
     }
     printf("\n\n~~~~~~~~~~~~~~~FINISH~~~~~~~~~~~~~~~~");
     getch();
     return 0;
 }

 /* 加在尾节点 */
 void Insert()
 {
     x=(struct student *)malloc(sizeof(struct student));
     printf("Please input your ID: ");
     scanf("%10d",&x->id);
     printf("Please input your score: ");
     scanf("%d",&x->score);
     x->next=NULL;

     if(head->next == NULL)
         head->next = x;
     else
     {
         /* 追踪链表的尾节点 */
         current = head->next;
         while(current->next != NULL)
             current = current->next;
         current->next = x;
     }
     printf("====================================\n");
 }

 /* 删除头节点 */
 void Delete()
 {
     char ch;

     if(head->next == NULL){
         printf("The queue is empty!\n");
         printf("====================================\n");
         return;
     }
     printf("Are you sure (y/n)? ");
     ch=getche();
     /* 确认是否要删除 */
     if(tolower(ch) == 'y')
     {
         current = head->next;
         head->next = current->next;
         printf("\n%d record has been deleted!!!", current->id);
         free(current);
     }
     printf("\n====================================\n");
 }

 void Display()
 {
     if(head->next == NULL)
         printf("The queue is empty!\n");
     else
     {
         /* 将head 指定给currnt，利用current指针将链表的所有节点输出 */
         current=head->next;
         while(current!=NULL)
         {
 printf("ID:%d, score=%d\n", current->id,
                               current->score);
             current=current->next;
         }
     }
     printf("====================================\n");
 }

 void Quit()
 {
     exit(0);
 }

栈

            

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 /* stack.c */
 /* 加入和删除都在链表的头节点 */
 #include <stdio.h>
 #include <conio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
 void Insert();
 void Delete();
 void Display();
 void Quit();
 struct student
 {
     int id;
     int score;
     struct student *next;
 };
 struct student *x,*head,*current;

 int main()
 {
     /* 链表的第一个节点不存放数据 */
     head=(struct student *)malloc(sizeof(struct student));
     head->next= NULL;
     for(;;) {
     int a;
     printf("\n");
     printf("1)Insert\n2)Delete\n3)Display\n4)Quit\n");
     printf("Which one: ");
     scanf("%d",&a);
     printf("\n");
     switch(a)
     {
     case 1:Insert();
     break;
     case 2:Delete();
     break;
     case 3:Display();
     break;
     case 4:Quit();
     break;
     }
     }
     printf("\n\n~~~~~~~~~~~~~~~FINISH~~~~~~~~~~~~~~~~");
     getch();
     return 0;
 }

 /* 加入一节点于链表头节点 */
 void Insert()
 {
     /* 分配内存，并指定数据 */
     x=(struct student *)malloc(sizeof(struct student));
     printf("Please input your ID: ");
     scanf("%d",&x->id);
     printf("Please input your score: ");
     scanf("%d",&x->score);
     x->next=NULL;

     x->next=head->next;
     head->next=x;
     printf("====================================\n");
 }

 /* 删除链表头节点的节点 */
 void Delete()
 {
     char ch;
     /* 判断链表是否有数据 */
     if(head->next == NULL)
     {
     printf("The stack is empty!\n");
     printf("====================================\n");
     return;
     }
     printf("Are you sure (y/n)? ");
     ch=getche();

     if(tolower(ch) == 'y')
       {
     current=head->next;
     printf("\n%d record has been deleted!!!", current->id);
     head->next=current->next;
     free(current);
     }
     printf("\n====================================\n");
 }

 void Display()
 {
     if(head->next == NULL)
     printf("The stack is empty!\n");
     else
     {
     current=head->next;
     while(current!=NULL)
     {
 printf("ID:%d, score=%d\n",current->id,current->
         score);
 current=current->next;
     }
     }
     printf("====================================\n");
 }

 void Quit()
 {
     exit(0);
 }

链表

        

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 /* singleListRandom.c */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <conio.h>

 void insert_func(void);
 void sort_func(void);
 void delete_func(void);
 void display_func(void);
 void modify_func(void);
 void anykey_func(void);

 struct student {
     char name[20];
     int score;
     struct student *next;
 };
 struct student *ptr, *head, *current, *prev;

 int main()
 {
     char option1;
     head = (struct student *) malloc(sizeof(struct student));
     head->next=NULL;
     while(1) {
         printf("\n");
         printf("******************\n");
         printf(" 1.insert\n");
         printf(" 2.delete\n");
         printf(" 3.display\n");
         printf(" 4.modify\n");
         printf(" 5.quit\n");
         printf("*******************\n");
         printf(" Enter your choice (1-5): ");
         option1=getche();
         printf("\n");
         switch(option1)    {
             case '1':
                 insert_func();
                 break;
             case '2':
                 delete_func();
                 break;
             case '3':
                 display_func();
                 break;
             case '4':
                 modify_func();
                 break;
             case '5':
                  printf("\n");
                 return 0;
         }
     }
 }

 /* 加入是以分数的高低加以排序 */
 void insert_func(void)
 {
     char s_temp[4];
     ptr=(struct student *) malloc(sizeof(struct student));
     printf(" Student name : ");
     gets(ptr->name);
     printf(" Student score: ");
     gets(s_temp);
     ptr->score = atoi(s_temp);

     prev = head;
     current = head->next;
     while ((current != NULL) && (current->score > ptr->score)) {
         prev = current;
         current = current->next;
     }
     ptr->next = current;
     prev->next = ptr;
 }

 /* 删除是以姓名为键值*/
 void delete_func(void)
 {
     char del_name[20], ans;
     printf(" Delete student name: ");
     gets(del_name);

     prev = head;
     current = head->next;
 while ((current != NULL) && (strcmp(current->name ,
         del_name)!=0)) {
         prev = current;
         current = current->next;
     }
     if (current != NULL) {
         /* 确认是否要删除 */
         printf(" Are you sure? ");
         ans=getche();
         if (ans == 'Y' || ans == 'y') {
             prev->next = current->next;
             free(current);
             printf(" Student %s has been deleted\n", del_name);
         }
     }
     else
         printf(" Student %s not found\n",del_name);
  }

 void modify_func(void)
 {
     char n_temp[20],s_temp[4];
     printf(" Modify student name: ");
     gets(n_temp);
     current=head->next;

 while ((current != NULL) && (strcmp(current->name , n_temp)!=0)) {
 prev = current;
      current = current->next;
     }
     if (current != NULL) {
         printf(" **************************\n");
         printf(" Student name : %s\n",current->name);
         printf(" Student score: %d\n",current->score);
         printf(" **************************\n");
         printf(" Please enter new score: ");
         gets(s_temp);
         current->score = atoi(s_temp);
         printf(" Student %s has been modified\n",n_temp);
     }
     else
         printf(" Student %s not found\n",n_temp);
 }

 void display_func(void)
 {
     int count=0;

     if(head->next == NULL) {
         printf(" No student record\n");
     }
     else {
         printf("\n");
         printf(" NAME SCORE\n");
         printf(" ----------------\n");
         current=head->next;
         while(current != NULL) {
 printf(" %-10s %3d\n", current->name,
         current->score);
             count++;
             current=current->next;
             if(count % 20 == 0) getch();
         }
         printf(" ----------------\n");
         printf(" Total %d record(s) found\n", count);
     }
 }