请用c语言设计一个图书登记管理程序。该程序应该具有下列功能： (1) 能从文件导入图书的信息 (2) 能从键盘录入图书的信息； (3) 给定图书号，显示某本图书信息； 能根据图书号修改图书的信息 能根据图书号删除图书的信息； 能特图书信息导出到指定文件

好的，这是一个关于图书登记管理的问题，我可以回答。以下是一个简单的C语言程序，可以实现这些功能：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_BOOKS 100

struct book {
    char id[20];
    char title[100];
    char author[50];
    int year;
    float price;
};

struct book books[MAX_BOOKS];
int num_books = 0;

void load_books(char *filename) {
    FILE *fp = fopen(filename, "r");
    if (fp == NULL) {
        printf("Error: cannot open file %s\n", filename);
        return;
    }
    while (num_books < MAX_BOOKS && fscanf(fp, "%s %s %s %d %f",
            books[num_books].id, books[num_books].title, books[num_books].author,
            &books[num_books].year, &books[num_books].price) == 5) {
        num_books++;
    }
    fclose(fp);
}

void save_books(char *filename) {
    FILE *fp = fopen(filename, "w");
    if (fp == NULL) {
        printf("Error: cannot open file %s\n", filename);
        return;
    }
    for (int i = 0; i < num_books; i++) {
        fprintf(fp, "%s %s %s %d %.2f\n",
            books[i].id, books[i].title, books[i].author,
            books[i].year, books[i].price);
    }
    fclose(fp);
}

void add_book() {
    if (num_books >= MAX_BOOKS) {
        printf("Error: too many books\n");
        return;
    }
    printf("Enter book ID: ");
    scanf("%s", books[num_books].id);
    printf("Enter book title: ");
    scanf("%s", books[num_books].title);
    printf("Enter book author: ");
    scanf("%s", books[num_books].author);
    printf("Enter book year: ");
    scanf("%d", &books[num_books].year);
    printf("Enter book price: ");
    scanf("%f", &books[num_books].price);
    num_books++;
}

void find_book() {
    char id[20];
    printf("Enter book ID: ");
    scanf("%s", id);
    for (int i = 0; i < num_books; i++) {
        if (strcmp(id, books[i].id) == 0) {
            printf("Book found:\n");
            printf("ID: %s\n", books[i].id);
            printf("Title: %s\n", books[i].title);
            printf("Author: %s\n", books[i].author);
            printf("Year: %d\n", books[i].year);
            printf("Price: %.2f\n", books[i].price);
            return;
        }
    }
    printf("Book not found\n");
}

void modify_book() {
    char id[20];
    printf("Enter book ID: ");
    scanf("%s", id);
    for (int i = 0; i < num_books; i++) {
        if (strcmp(id, books[i].id) == 0) {
            printf("Enter new book title (or press Enter to keep the same): ");
            scanf("%s", books[i].title);
            printf("Enter new book author (or press Enter to keep the same): ");
            scanf("%s", books[i].author);
            printf("Enter new book year (or press 0 to keep the same): ");
            scanf("%d", &books[i].year);
            printf("Enter new book price (or press 0 to keep the same): ");
            scanf("%f", &books[i].price);
            return;
        }
    }
    printf("Book not found\n");
}

void delete_book() {
    char id[20];
    printf("Enter book ID: ");
    scanf("%s", id);
    for (int i = 0; i < num_books; i++) {
        if (strcmp(id, books[i].id) == 0) {
            for (int j = i; j < num_books - 1; j++) {
                books[j] = books[j + 1];
            }
            num_books--;
            printf("Book deleted\n");
            return;
        }
    }
    printf("Book not found\n");
}

void export_book() {
    char id[20], filename[100];
    printf("Enter book ID: ");
    scanf("%s", id);
    for (int i = 0; i < num_books; i++) {
        if (strcmp(id, books[i].id) == 0) {
            printf("Enter filename to export: ");
            scanf("%s", filename);
            FILE *fp = fopen(filename, "w");
            if (fp == NULL) {
                printf("Error: cannot open file %s\n", filename);
                return;
            }
            fprintf(fp, "%s %s %s %d %.2f\n",
                books[i].id, books[i].title, books[i].author,
                books[i].year, books[i].price);
            fclose(fp);
            printf("Book exported to file %s\n", filename);
            return;
        }
    }
    printf("Book not found\n");
}

int main() {
    load_books("books.txt");
    while (1) {
        printf("Enter command (add, find, modify, delete, export, quit): ");
        char cmd[10];
        scanf("%s", cmd);
        if (strcmp(cmd, "add") == 0) {
            add_book();
        } else if (strcmp(cmd, "find") == 0) {
            find_book();
        } else if (strcmp(cmd, "modify") == 0) {
            modify_book();
        } else if (strcmp(cmd, "delete") == 0) {
            delete_book();
        } else if (strcmp(cmd, "export") == 0) {
            export_book();
        } else if (strcmp(cmd, "quit") == 0) {
            break;
        } else {
            printf("Invalid command\n");
        }
    }
    save_books("books.txt");
    return 0;
}

这个程序使用了一个结构体 `book` 来存储每本书的信息，包括图书号、书名、作者、出版年份和价格。程序可以从文件中导入图书信息，也可以从键盘录入图书信息。给定图书号，程序可以显示某本图书的信息，也可以根据图书号修改图书的信息或删除图书的信息。程序还可以将特定的图书信息导出到指定文件。