结构体

#include <stdio.h>
    4
    5 #define MAXTITL   40
    6 #define MAXAUTL   40
    7 #define MAXBKS   4              /* maximum number of books  */
    8
    9 struct book {                     /* set up book template     */
   10     char title[MAXTITL];
   11     char author[MAXAUTL];
   12     float value;
   13 };
   14
   15 int main(void)
   16 {
   17     struct book library[MAXBKS]; /* array of book structures */
   18     int count = 0;
   19     int index;
   20
   21     printf("Please enter the book title.\n");
  22     printf("Press [enter] at the start of a line to stop.\n");
  23     while (count < MAXBKS && gets(library[count].title) != NULL
   24                           && library[count].title[0] != '\0')
   25     {
    26         printf("Now enter the author.\n");
    27         gets(library[count].author);
   28         printf("Now enter the value.\n");
    29         scanf("%f", &library[count++].value);
    30   /          while (getchar() != '\n')
   31        /  continue;       //   [> clear input line         <]
   32        /*getchar();*/
   33         if (count < MAXBKS)
 34         printf("Enter the next title.\n");
   35     }
   36
   37     if (count > 0)
   38     {
 39         printf("Here is the list of your books:\n");
   40         for (index = 0; index < count; index++)
41         printf("%s by %s: $%.2f\n", library[index].title,
   42             library[index].author, library[index].value);
   43     }
   44     else
 45         printf("No books? Too bad.\n");
   46
   47     return 0;
   48 }

23,24行 ：
gets函数读入字符串，接收到EOF或者换行符结束，读取的换行符被转换成’\0‘ 空字符
gets的null有2种情况
1.feof ( end-of-file)
2.ferror ( read error)
输完value，回车第二次就会使title[0] = '\0' ,会直接结束。

30,31行：
吸收上一个回车，防止被下一个title读入

代码来源：c primer plus 383页