这个程序是一个通过软件工作的书库。问题是，当我按价格对书籍进行分类并打印出来时，它们永远不会被分类！
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
static int count;
struct book
{
int bookid;
char name[30];
char author[30];
float price;
};
struct book b[40];
void add(void);
void del(void);
void sort(void);
void price(void);
void print(void);
void main(void)
{
char choice;
while(1)
{
clrscr();
printf("Enter a choice:\n 1.Add a book.\n 2.Delete a book.\n 3.Sort books by price.\n 4.To print all books details.\n 5.To print the names of the books whose price is less than 1000.\n 6.Exit\n");
choice=getche();//doing by getch() as getche makes the program rough as it is printed
switch(choice)
{
case'1':add();break;
case'2':del();break;
case'3':sort();break;
case'4':print();break;
case'5':price();break;
case'6':exit(0);
default:printf("Enter a valid choice.");break;
}
}/*switch ends*/
}
void add(void)
{
int i;
char ch[30];
clrscr();
for(i=count;i<40;i++)
{
printf("Enter books name:\n");
gets(b[i].name);
printf("Enter author's name\n");
gets(b[i].author);
printf("Enter price:\n");
gets(ch);
b[i].price=atoi(ch);
b[i].bookid=count;
break;
} /* for ends*/
count++;
printf("Dear User,the book has succesfully been added.The book id is %d",b[i].bookid);
getch();
}
void print(void)
{
int i;
clrscr();
for(i=0;i<count;i++)
{
printf("Bookid=%d,Name=%s,Author=%s,Price=%f\n",b[i].bookid,b[i].name,b[i].author,b[i].price);
}
getch();
}
void del(void)
{
int i,j;
char ch[10];
clrscr();
printf("Enter book id:");
gets(ch); // how do i put it into the structure as i dont know that which structure it belongs to
for(i=0;i<count;i++) //searching
{
if(b[i].bookid==atoi(ch))
{
for(j=i;j<count;j++)
{
b[j]=b[j+1];
}//for j ends
} //if ends
} /* for of i ends */
count--;
// sort();
getch();
}
//void del(void)
//{
// int i;
// char ch[10];
// clrscr();
//printf("Enter book id:");
// gets(ch);
// for(i=0;i<40;i++)
// {
// b[i]=b[i+1];
//
// }
// count--;
// printf("Dear user,delete succesful");
//getch();
//}
void sort(void)
{
int in,out;
struct book temp;
for(out=0;out<count-1;out++)
{
for(in=out+1;out<count;out++)
{
if(b[out].price>b[in].price)
{
temp=b[out]
b[out]=b[in];
b[out]=temp;
}
}/*for out ends*/
}//for in ends
printf("Dear user,the books are sorted by price.\n");
getch();
}
void price(void)
{
int i;
clrscr();
for(i=0;i<count;i++)
{
if(b[i].price<1000)
{
printf("%d.%s\n",i+1,b[i].name);
}
}
getch();
答案 0 :(得分：4)
void sort(void)
{
int in,out;
struct book temp;
for(out=0;out<count-1;out++)
{
//**(in=out+1;out<count;out++)**//look here please
for(in=out+1;in<count;in++)
{
if(b[out].price>b[in].price)
{
temp=b[out]
b[out]=b[in];
b[in]=temp;//**b[out]=temp;**//look here plz
}
}/*for out ends*/
}//for in ends
printf("Dear user,the books are sorted by price.\n");
getch();
}
答案 1 :(得分：1)
除了错误之外的重大错误是不使用C库的qsort函数。除非您打算写一个非常好的排序（可能是快速排序，合并排序或堆排序，具体取决于您的具体需求），qsort会更好，并且需要更少的代码行。
答案 2 :(得分：0)
temp=b[out]
b[out]=b[in];
b[out]=temp;
应该是：
temp=b[out];
b[out] = b[in];
b[in] = temp;
答案 3 :(得分：0)
看起来像是
for(in=out+1;out<count;out++)
应该是
for(in=out+1;out<count;in++)
答案 4 :(得分：0)
这是一个经过测试的修正（我已经这样做了，所以你有一个概述，我认为，好的代码，而不是简化你的作业：你应该理解它而不是复制/粘贴它）。 对于您的问题，sort（）函数是最重要的。
#include <stdio.h>
/** Types *************************************************************/
//You should introduce constants, to allow quick changes
#define BOOK_NAME_LEN 30
#define NAME_LEN 30
#define PRICE_NUMBERS 4
#define LIBRARY_CAPACITY 100
//Allows to calculate ID numbers from library capacity (they're linked)
#define STRINGIZE(a) #a
#define STRINGIZE_CONSTANT(a) STRINGIZE(a)
#define ID_NUMBERS (sizeof(STRINGIZE_CONSTANT(\
LIBRARY_CAPACITY))/sizeof(char)-1)
typedef struct book Book;
struct book
{
//id is unsigned
size_t id;
char name[BOOK_NAME_LEN+1];
char author[NAME_LEN+1];
float price;
};
typedef struct library Library;
struct library {
Book books[LIBRARY_CAPACITY];
size_t inventory; //Book count
size_t id_cnt; //ID counter, never decremented
};
/** Input *************************************************************/
#include <string.h>
#include <stdlib.h>
//Purge stdin after removing ending \n
void clean(const char *buffer, FILE *fp)
{
char *p = strchr(buffer,'\n');
if (p != NULL) {
*p = 0;
}
else {
int c;
while ((c = fgetc(fp)) != '\n' && c != EOF);
}
}
//Gets a string from input without ending \n and
//with stdin purge
void get_str(char *str, size_t len) {
fgets(str, len+1, stdin);
clean(str, stdin);
}
//Explicit
int get_int_num(size_t n_digits) {
int ret = 0;
//Converts an entered string to integer
char *num = malloc((n_digits+1)*sizeof(char));
if(num !=NULL) {
get_str(num, n_digits);
ret = atoi(num);
free(num), num = NULL;
}
return ret;
}
//Explicit
float get_float_num(size_t n_digits) {
float ret = 0.f;
//The comma is a char
char *num = malloc((n_digits+2)*sizeof(char));
if(num !=NULL) {
get_str(num, n_digits+1);
ret = atof(num);
free(num), num = NULL;
}
return ret;
}
#include <math.h>
//Gets an integer choice in a range, useful for menus
int get_choice(int min, int max) {
int ret = 0;
do {
//The number of digits is deduced from
//max's one.
ret = get_int_num(log10(max)+1);
}while(ret < min || ret > max);
return ret;
}
/** Library functions **************************************************/
//Printing
void print_library(Library const * const library) {
for(size_t i = 0 ; i < library->inventory ; ++i) {
printf("%u) %s BY %s : %.2f USD\n", i+1, library->books[i].name,
library->books[i].author,
library->books[i].price);
}
}
/* Adding */
void add(Library * const library) {
//Fills infos
printf("Name ? ");
get_str(library->books[library->inventory].name, BOOK_NAME_LEN);
printf("Author ? ");
get_str(library->books[library->inventory].author, NAME_LEN);
printf("Price (%u significative numbers) ? ", PRICE_NUMBERS);
library->books[library->inventory].price = get_float_num(PRICE_NUMBERS);
//Unique id from internal library counter
library->books[library->inventory].id = ++library->id_cnt;
//And finally increments books count
library->inventory++;
}
/* End adding */
/* Deleting */
#include <stdbool.h>
//You will be able to remove by anything providing that you
//search the corresponding ID (then, same menu as for sorting)
bool remove_by_id(Library * const library, size_t id) {
bool ret = false;
for(size_t i = 0 ; i < library->inventory ; ++i) {
if(library->books[i].id == id) {
for(size_t j = i ; j < library->inventory-1 ; ++j) {
library->books[j] = library->books[j+1];
}
library->inventory--;
ret = true;
}
}
return ret;
}
void del(Library * const library) {
printf("ID ? ");
size_t id = get_int_num(ID_NUMBERS);
printf("Book %u %s.", id, remove_by_id(library, id) ?
"successfully deleted" :
"NOT deleted (probably wrong id)");
}
/* End deleting */
/* Sorting */
int cmp_by_price(void const *b1, void const *b2) {
return ((Book*)b1)->price >= ((Book*)b2)->price;
}
int cmp_by_author(void const *b1, void const *b2) {
return strcmp(((Book*)b1)->author, ((Book*)b2)->author);
}
int cmp_by_name(void const *b1, void const*b2) {
return strcmp(((Book*)b1)->name, ((Book*)b2)->name);
}
void sort(Library * const library) {
printf("Sort by :\n");
printf("1) Book name\n");
printf("2) Author name\n");
printf("3) Price\n");
printf("Your choice : ");
//Function pointer to use appropriate comparison function
int (*compare)(void const *, void const*) = NULL;
int choice = get_choice(1, 3);
switch(choice) {
case 3:
compare = cmp_by_price;
break;
case 2:
compare = cmp_by_author;
break;
case 1:
compare = cmp_by_name;
break;
default:
break;
}
qsort(library->books, library->inventory, sizeof(Book), compare);
printf("Sorted :\n");
print_library(library);
}
/* End sorting */
/** Main program ******************************************************/
#include <ctype.h>
bool stop() {
char c[1] = "";
printf("\nContinue (\'y\' for yes) ? ");
get_str(c, 1);
return tolower(c[0]) != 'y';
}
int main(void) {
//NEVER use global variables... Prefer to pass them through arguments
//(of course with pointers otherwise they won't be modified)
Library library = {{{0}}, 0, 0};
do {
printf("Actions available : \n");
printf("1) Add book\n");
printf("2) Delete book\n");
printf("3) Sort books\n");
printf("Your choice : ");
int choice = get_choice(1, 3);
switch(choice) {
case 1:
add(&library);
break;
case 2:
del(&library);
break;
case 3:
sort(&library);
break;
default:
break;
}
}while(!stop());
return 0;
}
如果您不理解某些内容，我们会在这里帮助您学习C.