内存分配的函数

void malloc(unsigned int size);创建长度为size的连续空间，返回一个起始地址的指针，如果创建内存空间失败返回NULL；
void calloc(unsigned n, unsigned size); 在内存的动态区存储中分配n个长度为size的连续空间，返回一个起始地址的指针，失败返回NULL；
void free(void p); 释放由p指向的内存区，使这部分内存区域能被其他变量使用，p使malloc或calloc函数时的返回值；
注意：在老版本C中，malloc和calloc返回的是char类型的指针，ANSI C返回的是 void 类型；

简单的链表

  1. #include <stdio.h>
  2. struct student {
  3.   long num;
  4.   float score;
  5.   struct student *next;
  6. };
  8. int main() {
  9.   struct student a,b,c, *head, *p;
  10.   a.num = 10001;
  11.   a.score = 100.00;
  12.   b.num = 10002;
  13.   b.score = 80.00;
  14.   c.num = 10003;
  15.   c.score = 95.00;
  16.   head = &a;
  17.   a.next = &b;
  18.   b.next = &c;
  19.   c.next = NULL;
  20.   p = head;
  21.   do {
  22.       printf("%ld %5.1f\n", p -> num, p -> score);
  23.     p = p -> next;
  24.   } while(p != NULL);
  25. }

链表

  1. #include<stdlib.h>
  2. #include<string.h>
  3. #include<stdio.h>
  5. #define LEN sizeof(struct student)
  7. struct student {
  8.     long num; // 学号
  9.   float score;
  10.   struct student *next;
  11. };
  13. int n;
  14. struct student *creat(void) { // 创建学生信息，输入0结束
  15.     struct student *head;
  16.     struct student *p1;
  17.     struct student *p2;
  18.     n = 0;
  19.     p1 = p2 = (struct student *) malloc(LEN); // 开辟一个新单元
  20.     scanf("%ld,%f", &p1 -> num, &p1 -> score);
  21.     head = NULL;
  22.     while (p1 -> num != 0) {
  23.         n += 1;
  24.         if (n == 1) { 
  25.             head = p1; 
  26.         } else {
  27.             p2 -> next = p1;
  28.         }
  29.         p2 = p1;
  30.         p1 = (struct student *) malloc(LEN);
  31.         scanf("%ld,%f", &p1 -> num, &p1 -> score);
  32.     }
  33.     p2 -> next = NULL;
  34.     return (head);
  35. }
  37. void print(struct student *head) {
  38.     struct student *p;
  39.   printf("\nNow, These %d records are:\n", n);
  40.   p = head;
  41.   if (p != NULL) {
  42.     do {
  43.       printf("%ld %5.1f\n", p -> num, p -> score);
  44.       p = p -> next;
  45.     } while (p != NULL);
  46.   }
  47. }
  49. struct student *del(struct student *head, long num) { // 按学号删除
  50.     struct student *p1, *p2;
  51.     if (head == NULL) {
  52.         printf("\nlist null! \n");
  53.       return (head);
  54.     }
  55.     p1 = head;
  56.     while (num != p1 -> num && p1 -> next != NULL) {
  57.         p2 = p1;
  58.         p1 = p1 -> next;
  59.     }
  60.     if (num == p1 -> num) {
  61.         if (p1 == head) {
  62.             head = p1 -> next;
  63.         } else {
  64.             p2 -> next = p1 -> next;
  65.         }
  66.         printf("delete: %ld\n", num);
  67.         n -= 1;
  68.     } else {
  69.         printf("%ld not been found!\n", num);
  70.     }
  71.     return (head);
  72. }
  74. struct student *insert(struct student *head, struct student *stud) {
  75.     struct student *p0, *p1, *p2;
  76.     p1 = head;
  77.     p0 = stud;
  78.     if (head == NULL) {
  79.         head = p0;
  80.         p0 -> next = NULL;
  81.     } else {
  82.         while ((p0 -> num > p1 -> num) && (p1 -> next != NULL)) {
  83.             p2 = p1;
  84.             p1 = p1 -> next;
  85.         }
  86.         if (p0 -> num <= p1 -> num) {
  87.             if (head == p1) {
  88.                 head = p0;
  89.             } else {
  90.                 p2 -> next = p0;
  91.             }
  92.             p0 -> next = p1;
  93.         } else {
  94.             p1 -> next = p0;
  95.           p0 -> next = NULL;
  96.         }
  97.     }
  98.     n += 1;
  99.     return (head);
  100. }
  102. int main(){
  103.     struct student *head, *stu;
  104.   long del_num;
  105.   printf("input records:\n");
  106.   head = creat();
  107.   print(head);
  108.   printf("\ninput the deleter number:");
  109.   scanf("%ld", &del_num);
  110.   while(del_num != 0) {
  111.     head = del(head, del_num);
  112.     print(head);
  113.     printf("\ninput the deleted number:");
  114.     scanf("%ld", &del_num);
  115.   }
  116.   printf("\ninput the inserted record:");
  117.   stu = (struct student *)malloc(LEN);
  118.   scanf("%ld,%f", &stu -> num, &stu -> score);
  119.   while(stu -> num != 0) {
  120.       head = insert(head, stu);
  121.     print(head);
  122.     printf("\ninput the inserted record:");
  123.     stu = (struct student *)malloc(LEN);
  124.     scanf("%ld,%f", &stu -> num, &stu -> score);
  125.   }
  126. }