C Primer Plus第十四章编程练习答案

学完C语言之后，我就去阅读《C Primer Plus》这本经典的C语言书籍，对每一章的编程练习题都做了相关的解答，仅仅代表着我个人的解答思路，如有错误，请各位大佬帮忙点出！

由于使用的是命令行参数常用于linux系统或者vscode，但此代码是运行于vs2022的，测试截图就不弄了。

1.重新编写复习题 5，用月份名的拼写代替月份号（别忘了使用 strcmp()）。在一个简单的程序中测试该函数。

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define LEN 12
struct month
{char name[10];char abbrev[4];int days;int monumb;
};
const struct month months[LEN] ={{"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 days(char* name)
{int i = 1;int num = 0;int total = 0;name[0] = toupper(name[0]);while (name[i] != '\0'){name[i] = tolower(name[i]);i++;}for (i = 0; i < LEN; i++){if (strcmp(name, months[i].name) == 0){num = months[i].monumb;break;}}if (num == 0){total = -1; }else{for (i = 0; i < num; i++){total += months[i].days;}}return total;
}
int main(void)
{int daytotal;char input[LEN];printf("Please enter the name of a month (q to quit): ");while (scanf("%s", input) == 1 && input[0] != 'q'){daytotal = days(input);if (daytotal > 0){printf("There are %d days through %s.\n", daytotal, input);}else{printf("%s isn't a valid month!\n", input);}printf("You can enter again (q to quit): ");while (getchar() != '\n')continue;}printf("Done.\n");return 0;
}

2.编写一个函数，提示用户输入日、月和年。月份可以是月份号、月份 名或月份名缩写。然后该程序应返回一年中到用户指定日子（包括这一天） 的总天数。

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#define LEN 12
struct month
{char name[10];char abbrev[4];int days;int monumb;
};struct month months[LEN] ={{"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}};
void is_leap_year(int year)
{if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0){months[1].days = 29;}
}
int days_result(char* month, int days)
{int i;int total = 0;int temp = atoi(month);if (days < 1 || days > 31){return -1;}if (0 == temp){month[0] = toupper(month[0]);for (i = 1; month[i] != '\0'; i++){month[i] = tolower(month[i]);}}for (i = 0; i < LEN; i++){if ((temp == months[i].monumb) ||(strcmp(month, months[i].name) == 0) ||(strcmp(month, months[i].abbrev) == 0)){if (days > months[i].days){return -1; }else{return total + days;}}else{total += months[i].days;}}return -1;
}
int main(void)
{int val;int day, year;char month[LEN];printf("Please enter day, month and year (q to quit): ");while (scanf("%d %s %d", &day, month, &year) == 3){is_leap_year(year);val = days_result(month, day);if (val > 0){printf("There are %d days from the beginning of %d to %s %d\n", val, year, month, day);}else{printf("You entered invalid datas!\n");}months[1].days = 28;printf("You can enter day, month and year again (q to quit): ");}printf("Done.\n");return 0;
}

3.修改程序清单 14.2 中的图书目录程序，使其按照输入图书的顺序输出 图书的信息，然后按照标题字母的声明输出图书的信息，最后按照价格的升 序输出图书的信息。

#include <stdio.h>
#include <string.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 100
struct book
{char title[MAXTITL];char author[MAXAUTL];float value;
};
void sort_title(struct book* pb[], int n)
{int i, j;struct book* temp;for (i = 0; i < n - 1; i++){for (j = i + 1; j < n; j++){if (strcmp(pb[j]->title, pb[i]->title) < 0){temp = pb[j];pb[j] = pb[i];pb[i] = temp;}}}
}
void sort_value(struct book* pb[], int n)
{int i, j;struct book* temp;for (i = 0; i < n - 1; i++){for (j = i + 1; j < n; j++){if (pb[j]->value < pb[i]->value){temp = pb[j];pb[j] = pb[i];pb[i] = temp;}}}
}
char* s_gets(char* st, int n)
{char* ret_val;char* find;ret_val = fgets(st, n, stdin);if (ret_val){find = strchr(st, '\n');if (find){*find = '\0';}else{while (getchar() != '\n')continue;}}return ret_val;
}
int main(void)
{struct book library[MAXBKS];struct book* book[MAXBKS];int count = 0;int index;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) && library[count].title[0] != '\0'){printf("Now enter the author.\n");s_gets(library[count].author, MAXAUTL);printf("Now enter the value.\n");scanf("%f", &library[count].value);book[count] = &library[count];count++;while (getchar() != '\n')continue;if (count < MAXBKS){printf("Enter the next title.\n");}}if (count > 0){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);}sort_title(book, count);printf("\nHere is the list of your books sorted by title letters:\n");for (index = 0; index < count; index++){printf("%s by %s: $%.2f\n", book[index]->title,book[index]->author, book[index]->value);}sort_value(book, count);printf("\nHere is the list of your books sorted by value(from low to high):\n");for (index = 0; index < count; index++){printf("%s by %s: $%.2f\n", book[index]->title,book[index]->author, book[index]->value);}}else{printf("No books? Too bad.\n");}return 0;
}

4.编写一个程序，创建一个有两个成员的结构模板：

a.第1个成员是社会保险号，第2个成员是一个有3个成员的结构，第1个 成员代表名，第2个成员代表中间名，第3个成员表示姓。创建并初始化一个 内含5个该类型结构的数组。该程序以下面的格式打印数据：

Dribble, Flossie M.–– 302039823

如果有中间名，只打印它的第1个字母，后面加一个点（.）；如果没有 中间名，则不用打印点。编写一个程序进行打印，把结构数组传递给这个函 数。

b.修改a部分，传递结构的值而不是结构的地址。

#include <stdio.h>
#include <string.h>
#define N 15
#define LEN 30
struct names
{char fname[N];char mname[N];char lname[N];
};
struct messages
{char ins_num[LEN];struct names name;
};
char* s_gets(char* st, int n)
{char* ret_val;char* find;ret_val = fgets(st, n, stdin);if (ret_val){find = strchr(st, '\n');if (find){*find = '\0';}else{while (getchar() != '\n')continue;}}return ret_val;
}
void show(const struct messages pt[], int n)
{int i;printf("All numbers messages:\n");for (i = 0; i < n; i++){if (pt[i].name.mname[0] == '\0'){printf("%s, %s", pt[i].name.fname, pt[i].name.lname);printf(" -- %s\n", pt[i].ins_num);}else{printf("%s, %s %c.", pt[i].name.fname, pt[i].name.lname, pt[i].name.mname[0]);printf(" -- %s\n", pt[i].ins_num);}}
}
int main(void)
{int count = 0;struct messages m[5];printf("Please enter the insurance number:\n");printf("Press [enter] at the start of a line to stop.\n");while (count < 5 && s_gets(m[count].ins_num, LEN) && m[count].ins_num[0] != '\0'){printf("Now enter the former name.\n");s_gets(m[count].name.fname, N);printf("Now enter the middle name(Without, [enter] to the next).\n");s_gets(m[count].name.mname, N);printf("Now enter the last name.\n");s_gets(m[count].name.lname, N);if (count++ < 5){printf("Enter the next insurance number:\n");}}if (count > 0){show(m, count);}else{printf("No data!\n");}return 0;
}

5.编写一个程序满足下面的要求。

a.外部定义一个有两个成员的结构模板name：一个字符串储存名，一个 字符串储存姓。

b.外部定义一个有3个成员的结构模板student：一个name类型的结构， 一个grade数组储存3个浮点型分数，一个变量储存3个分数平均数。

c.在main()函数中声明一个内含CSIZE（CSIZE = 4）个student类型结构的 数组，并初始化这些结构的名字部分。用函数执行g、e、f和g中描述的任 务。

d.以交互的方式获取每个学生的成绩，提示用户输入学生的姓名和分 数。把分数储存到grade数组相应的结构中。可以在main()函数或其他函数中 用循环来完成。

e.计算每个结构的平均分，并把计算后的值赋给合适的成员。

f.打印每个结构的信息。

g.打印班级的平均分，即所有结构的数值成员的平均值。

#include <stdio.h>
#include <string.h>
#define LEN 15
#define CSIZE 4
#define SCORES 3
struct name
{char fname[LEN];char lname[LEN];
};
struct student
{struct name mes;float grade[SCORES];float aver;
};
void set_students(struct student ar[], int n)
{int i, j;for (i = 0; i < n; i++){printf("Please enter three scores for %s %s:\n", ar[i].mes.fname, ar[i].mes.lname);for (j = 0; j < SCORES; j++){while (scanf("%f", &ar[i].grade[j]) != 1){while (getchar() != '\n')continue;printf("Please enter a number: ");}}}
}
void find_averages(struct student ar[], int n)
{int i, j;float sum;for (i = 0; i < n; i++){for (j = 0, sum = 0.0f; j < SCORES; j++){sum += ar[i].grade[j];}ar[i].aver = sum / SCORES;}
}
void show_messages(const struct student ar[], int n)
{int i, j;for (i = 0; i < n; i++){printf("\n%s %s's three scores: ", ar[i].mes.fname, ar[i].mes.lname);for (j = 0; j < SCORES; j++){printf("%g ", ar[i].grade[j]);}printf("\nAverage: %g\n", ar[i].aver);}
}
void show_averages(const struct student ar[], int n)
{int i;float total;for (i = 0, total = 0.0f; i < n; i++){total += ar[i].aver;}printf("\nClass average: %g\n", total / n);
}
int main(void)
{struct student classes[CSIZE] ={{"Flip", "Snide"},{"Clare", "Voyans"},{"Bingo", "Higgs"},{"Fawn", "Hunter"}};set_students(classes, CSIZE);find_averages(classes, CSIZE);show_messages(classes, CSIZE);show_averages(classes, CSIZE);return 0;
}

6.一个文本文件中保存着一个垒球队的信息。每行数据都是这样排列：

4 Jessie Joybat 5 2 1 1

第1项是球员号，为方便起见，其范围是0～18。第2项是球员的名。第3 项是球员的姓。名和姓都是一个单词。第4项是官方统计的球员上场次数。 接着3项分别是击中数、走垒数和打点（RBI）。文件可能包含多场比赛的 数据，所以同一位球员可能有多行数据，而且同一位球员的多行数据之间可 能有其他球员的数据。编写一个程序，把数据储存到一个结构数组中。该结 构中的成员要分别表示球员的名、姓、上场次数、击中数、走垒数、打点和 安打率（稍后计算）。可以使用球员号作为数组的索引。该程序要读到文件 结尾，并统计每位球员的各项累计总和。

世界棒球统计与之相关。例如，一次走垒和触垒中的失误不计入上场次 数，但是可能产生一个RBI。但是该程序要做的是像下面描述的一样读取和 处理数据文件，不会关心数据的实际含义。

要实现这些功能，最简单的方法是把结构的内容都初始化为零，把文件 中的数据读入临时变量中，然后将其加入相应的结构中。程序读完文件后， 应计算每位球员的安打率，并把计算结果储存到结构的相应成员中。计算安打率是用球员的累计击中数除以上场累计次数。这是一个浮点数计算。最 后，程序结合整个球队的统计数据，一行显示一位球员的累计数据。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LEN 19
typedef struct
{int id;           //球员的编号char fname[LEN];  //球员的名;char lname[LEN];  //球员的姓;int stage_num;    //球员的上场次数;int hit_num;      //球员的击中数;int base_num;     //球员的走垒数;int rbi;          //球员的打点;double hit_rate;  //球员的安打率;
} TEAM;
void read_datas(TEAM players[], int n, FILE* fp)
{int count = 0;char fname[LEN], lname[LEN];int m , stage_num, hit_num, base_num, rbi;while (fscanf(fp, "%d %18s %18s %d %d %d %d", &m, fname, lname, &stage_num, &hit_num, &base_num, &rbi) != EOF){if (players[count].stage_num == 0){++count;}strcpy(players[count].fname, fname);strcpy(players[count].lname, lname);players[count].id = m;players[count].stage_num += stage_num;players[count].hit_num += hit_num;players[count].base_num += base_num;players[count].rbi += rbi;}for (int i = 0; i < n; i++){players[i].hit_rate = 1.0 * players[i].hit_num / players[i].stage_num;}printf("Datas for all players:\n");printf("Id   First_name   Last_name   Stage   Hit_rate   Base_num   RBI   Hit_rate\n");for (int i = 0; i < n; i++){if (players[i].stage_num){printf("%-4d %-12s %-10s %5d %7d %11d %8d %8.2f\n",players[i].id, players[i].fname, players[i].lname,players[i].stage_num, players[i].hit_num, players[i].base_num,players[i].rbi, players[i].hit_rate);}}
}
int main(void)
{FILE* fp;fp = fopen("datas.txt", "r");if (fp == NULL){fprintf(stderr, "Can't open file datas.txt.\n");exit(-1);}static TEAM players[LEN];read_datas(players, LEN, fp); fclose(fp);

7.修改程序清单 14.14，从文件中读取每条记录并显示出来，允许用户 删除记录或修改记录的内容。如果删除记录，把空出来的空间留给下一个要 读入的记录。要修改现有的文件内容，必须用"r+b"模式，而不是"a+b"模 式。而且，必须更加注意定位文件指针，防止新加入的记录覆盖现有记录。 最简单的方法是改动储存在内存中的所有数据，然后再把最后的信息写入文 件。跟踪的一个方法是在book结构中添加一个成员表示是否该项被删除。

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 10
#define CONTINUE 0
#define DONE 1
struct book
{char title[MAXTITL];char author[MAXAUTL];float value;
};
struct pack
{struct book books;bool canceled;
};
int get_first(const char* str)
{int ch;ch = tolower(getchar());while (strchr(str, ch) == NULL){printf("Invalid data! Please enter again: ");eatline();ch = tolower(getchar());}eatline();return ch;
}int get_books(struct pack* pb)
{int status = CONTINUE;if (s_gets(pb->books.title, MAXTITL) == NULL || pb->books.title[0] == '\0'){status = 1;}else{printf("Now enter the author: ");s_gets(pb->books.author, MAXAUTL);printf("Now enter the value: ");while (scanf("%f", &pb->books.value) != 1){eatline();puts("Please enter a valid value: ");}eatline();pb->canceled = false;}return status;
}
void update(struct pack* item)
{int ch;struct book copy;copy = item->books;printf("============================================\n");printf("t) modify title a) modify author\n");printf("v) modify value s) quit, saving changes\n");printf("q) quit, ignore changes\n");printf("============================================\n");printf("Please you enter to choose: ");while ((ch = get_first("tavsq")) != 's' && ch != 'q'){switch (ch){case 't':{printf("Please enter new title: ");s_gets(copy.title, MAXTITL);break;}case 'a':{printf("Please enter new author: ");s_gets(copy.author, MAXAUTL);break;}case 'v':{printf("Please enter new value: ");while (scanf("%f", &copy.value) != 1){eatline();puts("Please enter a valid value: ");}eatline();break;}}printf("============================================\n");printf("t) modify title a) modify author\n");printf("v) modify value s) quit, saving changes\n");printf("q) quit, ignore changes\n");printf("============================================\n");printf("You can choose again: ");}if (ch == 's'){item->books = copy;}return;
}
char* s_gets(char* st, int n)
{char* ret_val;char* find;ret_val = fgets(st, n, stdin);if (ret_val){find = strchr(st, '\n');if (find){*find = '\0';}else{while (getchar() != '\n')continue;}}return ret_val;
}
void eatline(void)
{while (getchar() != '\n')continue;return;
}
int main(void)
{struct pack library[MAXBKS];int count = 0;int deleted = 0;int index, filecount, open;FILE* pbooks;int size = sizeof(struct book);if ((pbooks = fopen("book.dat", "rb")) != NULL){while (count < MAXBKS && fread(&library[count], size, 1, pbooks) == 1){if (count == 0){puts("Current contents of book.dat:");}printf("%s by %s: $%.2f\n", library[count].books.title,library[count].books.author, library[count].books.value);printf("Do you want to change or delete this entry(y/n)?\n");printf("Please you enter to choose: ");if (get_first("yn") == 'y'){printf("Enter c to change, d to delete entry: ");if (get_first("cd") == 'd'){library[count].canceled = true; deleted++;printf("Flag marked for deletion(The space for the next book).");}else{update(&library[count]); }}count++;}fclose(pbooks);}filecount = count - deleted; if (count == MAXBKS){printf("The book.dat file is full.\n");exit(-1);}if (deleted > 0){printf("If you delete some books, you should enter books to replace.\n");}printf("Please add new book titles.\n");printf("Press [enter] at the start of a line to stop.\n");open = 0;while (filecount < MAXBKS){if (filecount < count) {while (library[open].canceled == false){open++;}if (get_books(&library[open]) == DONE){break; }}else if (get_books(&library[filecount]) == DONE){break;}filecount++;if (filecount < MAXBKS){puts("Enter the next book title.");}}printf("Here is the list of your books:\n");for (index = 0; index < filecount; index++){if (library[index].canceled == false){printf("%s by %s: $%.2f\n", library[index].books.title,library[index].books.author, library[index].books.value);}}pbooks = fopen("book.dat", "wb");if (pbooks == NULL){printf("Can't open book.dat file for output.\n");exit(-1);}for (index = 0; index < filecount; index++){if (library[index].canceled == false){fwrite(&(library[index].books), size, 1, pbooks);}}fclose(pbooks);printf("Bye.\n");return 0;
}

8.巨人航空公司的机群由 12 个座位的飞机组成。它每天飞行一个航 班。根据下面的要求，编写一个座位预订程序。

a.该程序使用一个内含 12 个结构的数组。每个结构中包括：一个成员 表示座位编号、一个成员表示座位是否已被预订、一个成员表示预订人的 名、一个成员表示预订人的姓。

b.该程序显示下面的菜单：

To choose a function, enter its letter label:

a) Show number of empty seats

b) Show list of empty seats

c) Show alphabetical list of seats

d) Assign a customer to a seat assignment

e) Delete a seat assignment

f) Quit

c.该程序能成功执行上面给出的菜单。选择d)和e)要提示用户进行额外 输入，每个选项都能让用户中止输入。

d.执行特定程序后，该程序再次显示菜单，除非用户选择f)。

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define LEN 14
#define SEATS 12
typedef struct
{int seat_id;bool status;char last[LEN];char first[LEN];
} plane;
void eatline(void)
{while (getchar() != '\n')continue;
}
int get_first(void)
{int ch;do{ch = tolower(getchar());} while (isspace(ch));eatline();return ch;
}
char* s_gets(char* st, int n)
{char* ret_val;char* find;ret_val = fgets(st, n, stdin);if (ret_val){find = strchr(st, '\n');if (find){*find = '\0';}else{while (getchar() != '\n')continue;}}return ret_val;
}
int getmenu(void)
{int ch;printf("To choose a function, enter its letter label:\n");printf("a) Show number of empty seats\n");printf("b) Show list of empty seats\n");printf("c) Show alphabetical list of seat\n");printf("d) Assign a customer to a seat\n");printf("e) Delete a seat assignment\n");printf("f) Quit\n");printf("Please you enter to choose: ");while (ch = get_first(), NULL == strchr("abcdef", ch)){printf("Invalid data! Please you choose again: ");}return ch;
}
void sort(plane* array[], int n) //按照ASCII码进行座位排序;
{int i, j;plane* temp;for (i = 0; i < n - 1; i++){for (j = i + 1; j < n; j++){if (strcmp(array[j]->last, array[i]->last) < 0){temp = array[j];array[j] = array[i];array[i] = temp;}}}
}
int openings(const plane pl[], int n) //显示空座位的数量;
{int seat;int count = 0;for (seat = 0; seat < n; seat++){if (pl[seat].status == false){count++;}}return count;
}
void list_assign(plane* ps[], int n) //显示按照字母序列排序后的座位表;
{int i;if (openings(*ps, n) == SEATS){puts("All seats are empty.");}else{sort(ps, n);for (i = 0; i < SEATS; i++){if (ps[i]->status == true){printf("Seat %d: %s, %s\n", ps[i]->seat_id, ps[i]->last, ps[i]->first);}}}
}
void show_seats(const plane pl[]) //显示已分配的座位;
{int i;puts("Seats currently taken:");for (i = 0; i < SEATS; i++){if (pl[i].status == true){printf("Seat %d: %s, %s\n", pl[i].seat_id, pl[i].last, pl[i].first);}}
}
void makelist(const plane pl[], char* str, int kind) //为分配和删除座位提供当前处理的座位数;
{int seat;char temp[LEN];*str = '\0'; //清空str中的内容;for (seat = 0; seat < SEATS; seat++){if (pl[seat].status == kind){sprintf(temp, "%d ", pl[seat].seat_id);strcat(str, temp);}}
}
void show_empty_seats(const plane pl[], int n) //显示空座位的信息;
{char seating[3 * SEATS];if (openings(pl, n) == 0){printf("All seats are assigned\n");}else{makelist(pl, seating, false);printf("The following seats are available: ");puts(seating);}
}
void assign_seat(plane pl[], int n) //分配空余座位;
{int ch, seat, flag;char list[3 * SEATS];if (openings(pl, n) == false){printf("All seats are assigned. Can't assign again!\n");}else{makelist(pl, list, false);printf("Available seats: %s\n", list);printf("Which seat do you want? Please you enter from the lists: ");do{while (scanf("%d", &seat) != 1){eatline();printf("Seats: %s\n", list);printf("Enter a number from the lists: ");}if (seat < 1 || seat > SEATS || pl[seat - 1].status == true){printf("Seats: %s\n", list);printf("Enter a number from the lists: ");flag = 1;}else{flag = 0;}} while (1 == flag); //本循环判断并处理用户的错误输入;eatline();printf("Enter first name:\n");s_gets(pl[seat - 1].first, LEN);printf("Enter last name:\n");s_gets(pl[seat - 1].last, LEN);printf("%s %s assigned to seat %d.\n", pl[seat - 1].first, pl[seat - 1].last, seat);printf("Enter a to accept assignment, c to cancel it: ");ch = get_first();while (strchr("ac", ch) == NULL){printf("Please enter a or c: ");ch = get_first();}if (ch == 'a'){pl[seat - 1].status = true;printf("Passenger assigned to seat.\n");}else if (ch == 'c'){printf("Passenger not assigned.\n");}}
}
void delete_seat(plane pl[], int n) //删除已分配的座位;
{int ch, seat, flag;char list[3 * SEATS];if (openings(pl, n) == SEATS){puts("All seats already are empty. Can't delete!");}else{show_seats(pl);makelist(pl, list, true);printf("Enter the number of the seat to be deleted: ");do{while (scanf("%d", &seat) != 1){eatline();printf("Seats: %s\n", list);printf("Enter a number from the lists:");}if (seat < 1 || seat > SEATS || pl[seat - 1].status == false){printf("Seats: %s\n", list);printf("Enter a number from this list:");flag = 1;}else{flag = 0;}} while (1 == flag);eatline();printf("%s %s to be canceled for seat %d.\n", pl[seat - 1].first, pl[seat - 1].last, seat);printf("Enter d to delete assignment, a to abort: ");ch = get_first();while (strchr("da", ch) == NULL){printf("Please enter d or a: ");ch = get_first();}if (ch == 'd'){pl[seat - 1].status = false;puts("Passenger dropped.");}else if (ch == 'a'){puts("Passenger retained.");}}
}
int main(void)
{int i, choice;plane plane_seat[SEATS];plane* ps[SEATS];for (i = 0; i < SEATS; i++){ps[i] = &plane_seat[i];}for (i = 0; i < SEATS; i++){plane_seat[i].status = false;plane_seat[i].seat_id = i + 1;}while ((choice = getmenu()) != 'f'){switch (choice){case 'a':{printf("There are %d empty seats.\n", openings(plane_seat, SEATS));break;}case 'b':{show_empty_seats(plane_seat, SEATS);break;}case 'c':{list_assign(ps, SEATS);break;}case 'd':{assign_seat(plane_seat, SEATS);break;}case 'e':{delete_seat(plane_seat, SEATS);break;}}putchar('\n');}printf("Bye from Colossus Airlines!\n");return 0;
}

9.巨人航空公司（编程练习 8）需要另一架飞机（容量相同），每天飞 4 班（航班 102、311、444 和519）。把程序扩展为可以处理4个航班。用一 个顶层菜单提供航班选择和退出。选择一个特定航班，就会出现和编程练习 8类似的菜单。但是该菜单要添加一个新选项：确认座位分配。而且，菜单 中的退出是返回顶层菜单。每次显示都要指明当前正在处理的航班号。另 外，座位分配显示要指明确认状态。

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define LEN 14
#define SEATS 12typedef struct
{int seat_id;bool status;char last[LEN];char first[LEN];
} plane;int getmenu(int choice);
int get_first(void);
int openings(const plane pl[], int n);
void show_empty_seats(const plane pl[], int n);
void list_assign(plane *ps[], int n);
void assign_seat(plane pl[], int n);
void delete_seat(plane pl[], int n);
void show_seats(const plane pl[]);
void sort(plane *array[], int n);
void makelist(const plane pl[], char *str, int kind);
char *s_gets(char *st, int n);
void eatline(void);
void airline(int choice, plane *pl, plane *ps[]);
void init(plane *pl, plane *ps[]);
int show_airline_menu(void);
void confirm_seat(const plane pl[]);int main(void)
{int ch;plane airline_102[SEATS];plane airline_311[SEATS];plane airline_444[SEATS];plane airline_519[SEATS];plane *ps_102[SEATS];plane *ps_311[SEATS];plane *ps_444[SEATS];plane *ps_519[SEATS];init(airline_102, ps_102);init(airline_311, ps_311);init(airline_444, ps_444);init(airline_519, ps_519);while ((ch = show_airline_menu()) != 'q'){putchar('\n');switch (ch){case 'a':{airline(ch, airline_102, ps_102);break;}case 'b':{airline(ch, airline_311, ps_311);break;}case 'c':{airline(ch, airline_444, ps_444);break;}case 'd':{airline(ch, airline_519, ps_519);break;}}putchar('\n');}puts("Bye from Colossus Airlines!");return 0;
}void init(plane *pl, plane *ps[])
{int i;for (i = 0; i < SEATS; i++){ps[i] = &pl[i];}for (i = 0; i < SEATS; i++){pl[i].status = false;pl[i].seat_id = i + 1;}return;
}int show_airline_menu(void)
{int ch;puts("There are some airlines for you to choose.");puts("a) Airline 102.");puts("b) Airline 311.");puts("c) Airline 444.");puts("d) Airline 519.");puts("q) Quit the program.");printf("Please you enter to choose: ");ch = get_first();while (strchr("abcdq", ch) == NULL){printf("Please enter a, b, c, d or q: ");ch = get_first();}return ch;
}void airline(int choice, plane *pl, plane *ps[])
{int ch;while ((ch = getmenu(choice)) != 'f'){switch (ch){case 'a':{printf("There are %d empty seats.\n", openings(pl, SEATS));break;}case 'b':{show_empty_seats(pl, SEATS);break;}case 'c':{list_assign(ps, SEATS);break;}case 'd':{assign_seat(pl, SEATS);break;}case 'e':{delete_seat(pl, SEATS);break;}case 'g':{confirm_seat(pl);break;}}putchar('\n');}return;
}int getmenu(int choice)
{int ch;if (choice == 'a'){printf("The airline 102 is being processed.\n");}else if (choice == 'b'){printf("The airline 311 is being processed.\n");}else if (choice == 'c'){printf("The airline 444 is being processed.\n");}else if (choice == 'd'){printf("The airline 519 is being processed.\n");}puts("To choose a function, enter its letter label:");puts("a) Show number of empty seats");puts("b) Show list of empty seats");puts("c) Show alphabetical list of seat");puts("d) Assign a customer to a seat");puts("e) Delete a seat assignment");puts("f) Quit");puts("g) Confirm seat assignment");printf("Please you enter to choose: ");ch = get_first();while (strchr("abcdefg", ch) == NULL){printf("Please enter a, b, c, d, e, f or g: ");ch = get_first();}return ch;
}int get_first(void) //获取输入的第一个字符,丢弃剩余字符;
{int ch;do{ch = tolower(getchar());} while (isspace(ch));eatline();return ch;
}int openings(const plane pl[], int n) //显示空座位的数量;
{int seat;int count = 0;for (seat = 0; seat < n; seat++){if (pl[seat].status == false){count++;}}return count;
}void list_assign(plane *ps[], int n) //显示按照字母序列排序后的座位表;
{int i;if (openings(*ps, n) == SEATS){puts("All seats are empty.");}else{sort(ps, n);for (i = 0; i < SEATS; i++){if (ps[i]->status == true){printf("Seat %d: %s, %s\n", ps[i]->seat_id, ps[i]->last, ps[i]->first);}}}return;
}void show_seats(const plane pl[]) //显示已分配的座位;
{int i;puts("Seats currently taken:");for (i = 0; i < SEATS; i++){if (pl[i].status == true){printf("Seat %d: %s, %s\n", pl[i].seat_id, pl[i].last, pl[i].first);}}return;
}void confirm_seat(const plane pl[]) //确认座位分配;
{int i;puts("Seats assignment lists:");for (i = 0; i < SEATS; i++){if (pl[i].status == true){printf("Seat %-2d: assigned.\n", pl[i].seat_id);}else{printf("Seat %-2d: unassigned.\n", pl[i].seat_id);}}return;
}void sort(plane *array[], int n) //按照ASCII码进行座位排序;
{int i, j;plane *temp;for (i = 0; i < n - 1; i++){for (j = i + 1; j < n; j++){if (strcmp(array[j]->last, array[i]->last) < 0){temp = array[j];array[j] = array[i];array[i] = temp;}}}return;
}char *s_gets(char *st, int n)
{char *ret_val;char *find;ret_val = fgets(st, n, stdin);if (ret_val){find = strchr(st, '\n');if (find){*find = '\0';}else{while (getchar() != '\n')continue;}}return ret_val;
}void eatline(void)
{while (getchar() != '\n')continue;return;
}void show_empty_seats(const plane pl[], int n) //显示空座位的信息;
{char seating[3 * SEATS];if (openings(pl, n) == 0){puts("All seats are assigned");}else{makelist(pl, seating, false);printf("The following seats are available: ");puts(seating);}return;
}void makelist(const plane pl[], char *str, int kind) //为分配和删除座位提供当前处理的座位数;
{int seat;char temp[LEN];*str = '\0'; //清空str中的内容;for (seat = 0; seat < SEATS; seat++){if (pl[seat].status == kind){sprintf(temp, "%d ", pl[seat].seat_id);strcat(str, temp);}}return;
}void assign_seat(plane pl[], int n) //分配空余座位;
{int ch, seat, flag;char list[3 * SEATS];if (openings(pl, n) == false){puts("All seats are assigned. Can't assign again!");}else{makelist(pl, list, false);printf("Available seats: %s\n", list);printf("Which seat do you want? Please you enter from the lists: ");do{while (scanf("%d", &seat) != 1){eatline();printf("Seats: %s\n", list);printf("Enter a number from the lists: ");}if (seat < 1 || seat > SEATS || pl[seat - 1].status == true){printf("Seats: %s\n", list);printf("Enter a number from the lists: ");flag = 1;}else{flag = 0;}} while (1 == flag); //本循环判断并处理用户的错误输入;eatline();puts("Enter first name:");s_gets(pl[seat - 1].first, LEN);puts("Enter last name:");s_gets(pl[seat - 1].last, LEN);printf("%s %s assigned to seat %d.\n", pl[seat - 1].first, pl[seat - 1].last, seat);printf("Enter a to accept assignment, c to cancel it: ");ch = get_first();while (strchr("ac", ch) == NULL){printf("Please enter a or c: ");ch = get_first();}if (ch == 'a'){pl[seat - 1].status = true;puts("Passenger assigned to seat.");}else if (ch == 'c'){puts("Passenger not assigned.");}}return;
}void delete_seat(plane pl[], int n) //删除已分配的座位;
{int ch, seat, flag;char list[3 * SEATS];if (openings(pl, n) == SEATS){puts("All seats already are empty. Can't delete!");}else{show_seats(pl);makelist(pl, list, true);printf("Enter the number of the seat to be deleted: ");do{while (scanf("%d", &seat) != 1){eatline();printf("Seats: %s\n", list);printf("Enter a number from the lists:");}if (seat < 1 || seat > SEATS || pl[seat - 1].status == false){printf("Seats: %s\n", list);printf("Enter a number from this list:");flag = 1;}else{flag = 0;}} while (1 == flag);eatline();printf("%s %s to be canceled for seat %d.\n", pl[seat - 1].first, pl[seat - 1].last, seat);printf("Enter d to delete assignment, a to abort: ");ch = get_first();while (strchr("da", ch) == NULL){printf("Please enter d or a: ");ch = get_first();}if (ch == 'd'){pl[seat - 1].status = false;puts("Passenger dropped.");}else if (ch == 'a'){puts("Passenger retained.");}}return;
}

10.编写一个程序，通过一个函数指针数组实现菜单。例如，选择菜单 中的 a，将激活由该数组第 1个元素指向的函数。

#include <stdio.h>
#include <math.h>
#include <ctype.h>
#include <string.h>
#define NUM 4
void eatline(void)
{while (getchar() != '\n')continue;
}
int get_first(void)
{int ch;do{ch = tolower(getchar());} while (isspace(ch));eatline();return ch;
}
int showmenu(void)
{int ch;printf("+-------------------------------+\n");printf("|a) double               b) half|\n");printf("|c) square               d) sqrt|\n");printf("|q) quit                        |\n");printf("+-------------------------------+\n");printf("Please you choose: ");while (ch = get_first(), NULL == strchr("abcdq", ch)){printf("Please enter a, b, c, d or q: ");}return ch;
}
double twice(double x)
{return 2.0 * x;
}
double half(double x)
{return x / 2.0;
}
double square(double x)
{return x * x;
}
void show(int i, double x, double (*pf[NUM])(double))
{x = (*pf[i])(x);printf("After operating: %g\n\n", x);
}
int main(void)
{int choice;double number;double (*pf[NUM])(double) = { twice, half, square, sqrt };while ((choice = showmenu()) != 'q'){printf("Please enter a number: ");while (scanf("%lf", &number) != 1){eatline();printf("Please enter again: ");}switch (choice){case 'a':{show(0, number, pf);break;}case 'b':{show(1, number, pf);break;}case 'c':{show(2, number, pf);break;}case 'd':{show(3, number, pf);break;}}}printf("Done.\n");return 0;
}

11.编写一个名为transform()的函数，接受4个参数：内含double类型数据 的源数组名、内含double类型数据的目标数组名、一个表示数组元素个数的 int类型参数、函数名（或等价的函数指针）。transform()函数应把指定函数 应用于源数组中的每个元素，并把返回值储存在目标数组中。例如：

transform(source, target, 100, sin);

该声明会把target[0]设置为sin(source[0])，等等，共有100个元素。在一 个程序中调用transform()4次，以测试该函数。分别使用math.h函数库中的两 个函数以及自定义的两个函数作为参数。

#include <stdio.h>
#include <math.h>
#define LEN 5
double square(double x)
{return x * x;
}
double triple(double x)
{return x * x * x;
}
void transform(double x[], double y[], int n, double (*p)(double))
{for (int i = 0; i < n; i++){y[i] = p(x[i]);}
}
void show_array(double temp[], int n)
{for (int i = 0; i < n; i++){printf("%g ", temp[i]);}printf("\n");
}
int main(void)
{double x[LEN] = { 2.0, 4.0, 6.0, 8.0, 9.0 }, y[LEN] = { 0.0 };printf("array:\n");show_array(x, LEN);printf("target array:\n");show_array(y, LEN);transform(x, y, LEN, sqrt);printf("After square root:\n");show_array(y, LEN);transform(x, y, LEN, cbrt);printf("After opening cube:\n");show_array(y, LEN);transform(x, y, LEN, square);printf("After square:\n");show_array(y, LEN);transform(x, y, LEN, triple);printf("After cube:\n");show_array(y, LEN);return 0;
}