学校图书馆新进一批图书，请用C语言编写软件以存储这些图书的信息。图书信息主要指：图书名称，出版社，数量，单价。软件应具备以下主要功能：(1) 数据输入。即，能够输入图书信息。(2) 数据保存。即，能够将输入的信息以文件的形式保存到计算机中。(3) 数据查询。即，能够按照“图书名称”查询图书信息，也能够按照“单价”查询图书信息。(4) 数据修改。即，当输入数据出现误操作时，事后可以更改。软件至少应具有“数据输入”、“保存”、“查询”、“修改”、“退出”5项菜单。

好的，以下是C语言代码实现：

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

#define MAX_BOOKS 100

struct book {
    char name[50];
    char publisher[50];
    int quantity;
    float price;
};

void save_books(struct book *books, int num_books);
void load_books(struct book *books, int *num_books);
void add_book(struct book *books, int *num_books);
void search_book(struct book *books, int num_books);
void modify_book(struct book *books, int num_books);

int main() {
    struct book books[MAX_BOOKS];
    int num_books = 0;
    int choice;

    load_books(books, &num_books);

    do {
        printf("\nMenu:\n");
        printf("1. Add book\n");
        printf("2. Save books\n");
        printf("3. Search book\n");
        printf("4. Modify book\n");
        printf("5. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                add_book(books, &num_books);
                break;
            case 2:
                save_books(books, num_books);
                break;
            case 3:
                search_book(books, num_books);
                break;
            case 4:
                modify_book(books, num_books);
                break;
            case 5:
                break;
            default:
                printf("Invalid choice\n");
        }
    } while (choice != 5);

    return 0;
}

void save_books(struct book *books, int num_books) {
    FILE *fp;
    int i;

    fp = fopen("books.dat", "wb");
    if (fp == NULL) {
        printf("Error creating file\n");
        return;
    }

    fwrite(&num_books, sizeof(int), 1, fp);
    fwrite(books, sizeof(struct book), num_books, fp);

    fclose(fp);

    printf("%d books saved to file\n", num_books);
}

void load_books(struct book *books, int *num_books) {
    FILE *fp;
    int i;

    fp = fopen("books.dat", "rb");
    if (fp == NULL) {
        printf("File not found\n");
        return;
    }

    fread(num_books, sizeof(int), 1, fp);
    fread(books, sizeof(struct book), *num_books, fp);

    fclose(fp);

    printf("%d books loaded from file\n", *num_books);
}

void add_book(struct book *books, int *num_books) {
    struct book new_book;

    printf("Enter book name: ");
    scanf("%s", new_book.name);
    printf("Enter publisher: ");
    scanf("%s", new_book.publisher);
    printf("Enter quantity: ");
    scanf("%d", &new_book.quantity);
    printf("Enter price: ");
    scanf("%f", &new_book.price);

    books[*num_books] = new_book;
    (*num_books)++;

    printf("Book added\n");
}

void search_book(struct book *books, int num_books) {
    int choice;
    char name[50];
    float price;
    int i;

    printf("Search by:\n");
    printf("1. Book name\n");
    printf("2. Price\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);

    switch (choice) {
        case 1:
            printf("Enter book name: ");
            scanf("%s", name);

            for (i = 0; i < num_books; i++) {
                if (strcmp(books[i].name, name) == 0) {
                    printf("Book found:\n");
                    printf("Name: %s\n", books[i].name);
                    printf("Publisher: %s\n", books[i].publisher);
                    printf("Quantity: %d\n", books[i].quantity);
                    printf("Price: %.2f\n", books[i].price);
                    return;
                }
            }

            printf("Book not found\n");
            break;
        case 2:
            printf("Enter price: ");
            scanf("%f", &price);

            for (i = 0; i < num_books; i++) {
                if (books[i].price == price) {
                    printf("Book found:\n");
                    printf("Name: %s\n", books[i].name);
                    printf("Publisher: %s\n", books[i].publisher);
                    printf("Quantity: %d\n", books[i].quantity);
                    printf("Price: %.2f\n", books[i].price);
                    return;
                }
            }

            printf("Book not found\n");
            break;
        default:
            printf("Invalid choice\n");
    }
}

void modify_book(struct book *books, int num_books) {
    char name[50];
    int i;

    printf("Enter book name to modify: ");
    scanf("%s", name);

    for (i = 0; i < num_books; i++) {
        if (strcmp(books[i].name, name) == 0) {
            printf("Enter new book name: ");
            scanf("%s", books[i].name);
            printf("Enter new publisher: ");
            scanf("%s", books[i].publisher);
            printf("Enter new quantity: ");
            scanf("%d", &books[i].quantity);
            printf("Enter new price: ");
            scanf("%f", &books[i].price);

            printf("Book modified\n");
            return;
        }
    }

    printf("Book not found\n");
}

这个程序使用结构体来存储每本书的信息，使用文件来保存和读取图书信息。用户可以选择添加新书、保存图书信息、查询图书信息、修改图书信息或退出程序。在查询和修改图书信息时，可以按照书名或单价进行搜索。