C Primer Plus 第六版(中文版)第十四章(注释版)编程练习答案
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14.18.1
#include<stdio.h>
#include<string.h>
#include<ctype.h>
struct month
{
char monthname[10];
char abbrev[5];
int days;
int num_month;
};
const struct month months[12] =
{
{
"January", "Jan", 31, 1},
{
"February", "Feb", 28, 2},
{
"March", "Mar", 31, 3},
{
"April", "Apr", 30, 4},
{
"May", "May", 31, 5},
{
"June", "Jun", 30, 6},
{
"July", "Jul", 31, 7},
{
"August", "Aug", 31, 8},
{
"September", "Sep", 30, 9},
{
"October", "Oct", 31, 10},
{
"November", "Nov", 30, 11},
{
"December", "Dec", 31, 12}
};
char * s_gets(char *st, int n);
int days(char * pt);
int main(void)
{
char input[20];
int total;
puts("输入月份名字:");
while (s_gets(input, 20) != NULL && input[0] != '\0')
{
total = days(input);//统计输入的月份有多少天
printf("我们有 %d 天，月份名称 %s.\n", total, input);
printf("next month (empty line to quit)\n");
}
puts("bye");
return 0;
}
int days(char * pt)//传递进去一个字符串，指针pt指向（数组）字符串
{
int i;
int mon_num = 0;//月份号
int total = 0;
pt[0] = toupper(pt[0]);//取出第一个字符转化成大写再赋给本身
for (int i = 1; pt[i] != '\0'; i++)//碰到空字符\0再停止，一直输出字符串里的字符
{
pt[i] = tolower(pt[i]);//剩余字符转为小写
}
for (i = 0; i < 12; i++)
{
if (strcmp(pt, months[i].monthname) == 0)//pt指针指向的（人为输入的）字符串与结构体中已有的月份进行比较
{
mon_num = months[i].num_month;//找到月份
}
}
for( i = 0; i < mon_num; i ++)//对找到的月份的天数求和
{
total += months[i].days;
}
return total;
}
char * s_gets(char *st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n ,stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
{
i++;
if (st[i] == '\n')
{
st[i] == '\0';
}
else
while (getchar() != '\n')
{
continue;
}
}
}
return ret_val;
}
14.18.2
在这里插入
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
char * s_gets(char *st, int n);
int days(int year, int month, int days);
int leapyear(int year);
struct month
{
char monthname[10];
char abbrev[5];
int days;
int num_month;
};
struct month months[12] =
{
{
"January", "Jan", 31, 1},
{
"February", "Feb", 28, 2},
{
"March", "Mar", 31, 3},
{
"April", "Apr", 30, 4},
{
"May", "May", 31, 5},
{
"June", "Jun", 30, 6},
{
"July", "Jul", 31, 7},
{
"August", "Aug", 31, 8},
{
"September", "Sep", 30, 9},
{
"October", "Oct", 31, 10},
{
"November", "Nov", 30, 11},
{
"December", "Dec", 31, 12}
};
int main(void)
{
int year, month, day;
char mname[10];
int i;
puts("请输入年：");
while (scanf_s("%d", &year) == 1)//输入正确返回值为1
{
puts("请输入月份：");
if (scanf_s("%d", &month) == 1)//按数字输入
{
printf("\n");
}
else//那么我们可能输入的是字符串了现在
{
s_gets(mname, 10);
for (i = 0; i < 12; i++)//那么就需要和12个月的全称去比较了，看看输入的那一个月
{
if (strcmp(mname, months[i].monthname) == 0 || strcmp(mname, months[i].abbrev))//全称、简称都一样
{
month = months[i].num_month;//找到了我们想找到的对应月份
break;
}
}
}
puts("请输入日期：");
if (scanf_s("%d", &day) != 1)//输入错误
{
exit(1);
}
printf("%d 天我们有。\n", days(year, month, day));
while (getchar()!='\n')//跳过多余输入
{
continue;
}
puts("请输入下一组要查看信息：q来退出");
}
puts("bye.");
return 0;
}
int days(int year,int month,int days)
{
int total = 0;
int i;
leapyear(year) ? (months[1].days = 29) : (months[1].days = 28);//判断是不是闰年,是那么二月份29天，
for (i = 0; i < month - 1; i++)//数据统计1-3月份(不可能+到3月份全部所以-1)，假定计算3.8月份的天数和，把1、2月份的日期+3月份的8天
{
total += months[i].days;
}
return total + days;//+的是当前3月份的天数
}
int leapyear(int year)//对闰年判断，返回1真，0假
{
if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))//对闰年判断
{
return 1;
}
else
return 0;
}
char * s_gets(char *st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n ,stdin);
if (ret_val!= NULL)
{
while (st[i] != '\n' && st[i] != '\0')
{
i++;
if (st[i] == '\n')
{
st[i] == '\0';
}
else
while (getchar() != '\n')
{
continue;
}
}
}
return ret_val;
}代码片
14.18.3
在这里插入代码片
#include <stdio.h>
#include <string.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 100
char * s_gets(char *st, int n);
struct book
{
char title[MAXTITL];
char author[MAXAUTL];
float value;
};
int main(void)
{
struct book library[MAXBKS];
int count = 0;
int index;
int seek, top;
struct book temp;
printf("Please enter the book title.\n");
printf("Press [enter] at the start of a line to stop.\n");
while ( count < MAXBKS && s_gets(library[count].title, MAXTITL) != NULL && library[count].title[0] != '\0')//循环录入信息
{
printf("Now enter the author.\n");
s_gets(library[count].author,MAXAUTL);//内容不为空，可以开始输入作者
printf("Now enter the value.\n");
scanf_s("%f", &library[count++].value);//数量自增加，每次循环加一次
while (getchar() != '\n')
continue;
if (count < MAXBKS)//书本数量未到上限
{
printf("Enter the next title.\n");
}
}
if (count > 0)//有书
{
printf("Here is the list of your books:\n");
for (index = 0; index < count; index++)
{
printf("%s by %s: $%.2f\n", library[index].title,
library[index].author, library[index].value);//循环把所有书本的详细信息输出
}
printf("............................................\n");
printf("Here is the list of your books sorted by value(from low to high):\n");
for (top = 0; top < count -1; top++)//外层--对价格进行比较，循环嵌套的方式：第一本开始
{
for (seek = top + 1; seek < count; seek++)//内层--第二本书和第一本比：第二本开始
{
if(library[top].value > library[seek].value)//第一本书价格大于比较的这本书
{
//交换过程,1与2,1与3，1与4....使得第一本永远是最便宜的
temp = library[top];
library[top] = library[seek];
library[seek] = temp;
}
}
}
for (index = 0; index < count; index++)
{
printf("%s by %s: $%.2f\n", library[index].title,
library[index].author, library[index].value);//循环把所有书本的详细信息输出
}
printf("............................................\n");
printf("Here is the list of your books sorted by title letters:\n");
for (top = 0; top < count - 1; top++)
{
for (seek = top + 1; seek < count; seek++)
{
if (strcmp(library[top].author, library[seek].author) > 0)//字符串比较
{
temp = library[top];
library[top] = library[seek];
library[seek] = temp;
}
}
}
for (index = 0; index < count; index++)
{
printf("%s by %s: $%.2f\n", library[index].title,
library[index].author, library[index].value);//循环把所有书本的详细信息输出
}
}
else
{
printf("No books? Too bad.\n");
}
return 0;
}
char * s_gets(char *st, int n)
{
char * ret_val;
char *find;
ret_val = fgets(st, n, stdin);
if (ret_val !=NULL)
{
find = strchr(st, '\n');
if (find)
{
*find = '\0';
}
else
while (getchar() != '\n') //清除IO缓冲区
continue;
}
return ret_val;
}