C语言文具销售，有简单的菜单，实现信息录入功能，在已有信息上添加新的记录，能够删除指定商品编号的记录，能够按编号查询设备，能够计算当日销售额，创建的链表或数组可存储于文件中，并能从文件中读取所存储的数据。带注释

以下是一个简单的C语言程序，实现了你描述的功能，并附有注释说明：

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

// 定义商品结构体
typedef struct {
    int id;             // 商品编号
    char name[50];      // 商品名称
    float price;        // 商品价格
} Product;

// 定义链表节点结构体
typedef struct Node {
    Product product;    // 商品信息
    struct Node* next;  // 下一个节点指针
} Node;

// 全局变量 - 链表头指针
Node* head = NULL;

// 函数声明
void displayMenu();
void addProduct();
void deleteProduct();
void searchProduct();
void calculateSales();
void saveDataToFile();
void loadDataFromFile();

int main() {
    int choice;
    
    loadDataFromFile();  // 从文件中加载数据
    
    do {
        displayMenu();  // 显示菜单
        printf("Enter your choice: ");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                addProduct();
                break;
            case 2:
                deleteProduct();
                break;
            case 3:
                searchProduct();
                break;
            case 4:
                calculateSales();
                break;
            case 5:
                saveDataToFile();
                break;
            case 6:
                loadDataFromFile();
                break;
            case 0:
                printf("Exiting program.\n");
                break;
            default:
                printf("Invalid choice. Please try again.\n");
        }
        
        printf("\n");
    } while (choice != 0);
    
    return 0;
}

// 显示菜单选项
void displayMenu() {
    printf("========== Menu ==========\n");
    printf("1. Add product\n");
    printf("2. Delete product\n");
    printf("3. Search product\n");
    printf("4. Calculate sales\n");
    printf("5. Save data to file\n");
    printf("6. Load data from file\n");
    printf("0. Exit\n");
}

// 添加商品
void addProduct() {
    Node* newNode = (Node*)malloc(sizeof(Node));
    
    printf("Enter product ID: ");
    scanf("%d", &newNode->product.id);
    
    printf("Enter product name: ");
    scanf("%s", newNode->product.name);
    
    printf("Enter product price: ");
    scanf("%f", &newNode->product.price);
    
    newNode->next = head;
    head = newNode;
    
    printf("Product added successfully.\n");
}

// 删除商品
void deleteProduct() {
    int id;
    
    if (head == NULL) {
        printf("No products available.\n");
        return;
    }
    
    printf("Enter product ID to delete: ");
    scanf("%d", &id);
    
    Node* current = head;
    Node* prev = NULL;
    
    while (current != NULL) {
        if (current->product.id == id) {
            if (prev == NULL) {
                // 删除头节点
                head = current->next;
            } else {
                // 删除中间或尾部节点
                prev->next = current->next;
            }
            
            free(current);
            printf("Product deleted successfully.\n");
            return;
        }
        
        prev = current;
        current = current->next;
    }
    
    printf("Product not found.\n");
}

// 查询商品
void searchProduct() {
    int id;
    
    if (head == NULL) {
        printf("No products available.\n");
        return;
    }
    
    printf("Enter product ID to search: ");
    scanf("%d", &id);
    
    Node* current = head;
    
    while (current != NULL) {
        if (current->product.id == id) {
            printf("Product found:\n");
            printf("ID: %d\n", current->product.id);
            printf("Name: %s\n", current->product.name);
            printf("Price: %.2f\n", current->product.price);
            return;
        }
        
        current = current->next;
    }
    
    printf("Product not found.\n");
}

// 计算销售额
void calculateSales() {
    float totalSales = 0;
    
    Node* current = head;
    
    while (current != NULL) {
        totalSales += current->product.price;
        current = current->next;
    }
    
    printf("Total sales: %.2f\n", totalSales);
}

// 将数据保存到文件
void saveDataToFile() {
    FILE* file = fopen("data.txt", "w");
    
    if (file == NULL) {
        printf("Failed to open file.\n");
        return;
    }
    
    Node* current = head;
    
    while (current != NULL) {
        fprintf(file, "%d,%s,%.2f\n", current->product.id, current->product.name, current->product.price);
        current = current->next;
    }
    
    fclose(file);
    printf("Data saved to file.\n");
}

// 从文件中加载数据
void loadDataFromFile() {
    FILE* file = fopen("data.txt", "r");
    
    if (file == NULL) {
        printf("Failed to open file.\n");
        return;
    }
    
    char line[100];
    
    // 清空链表
    while (head != NULL) {
        Node* temp = head;
        head = head->next;
        free(temp);
    }
    
    // 逐行读取文件并创建链表节点
    while (fgets(line, sizeof(line), file) != NULL) {
        Node* newNode = (Node*)malloc(sizeof(Node));
        sscanf(line, "%d,%[^,],%f", &newNode->product.id, newNode->product.name, &newNode->product.price);
        newNode->next = head;
        head = newNode;
    }
    
    fclose(file);
    printf("Data loaded from file.\n");
}

请注意，此示例只是一个基本实现，可能需要根据实际需求进行进一步修改和完善。例如，可以添加输入验证、错误处理和其他功能。另外，此示例使用了简单的链表数据结构来存储商品信息，你还可以尝试使用数组或其他数据结构来实现。