使用c语言写一串代码实现商品库存管理系统，要求用到文本文件

好的，以下是一个简单的商品库存管理系统的C语言代码示例：

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

#define MAX_ITEMS 100 // 最大商品数量
#define MAX_NAME_LEN 50 // 商品名称最大长度

typedef struct {
    int id;
    char name[MAX_NAME_LEN];
    int quantity;
} Item;

int read_items(Item items[]) {
    FILE *fp;
    fp = fopen("items.txt", "r");
    if (fp == NULL) {
        printf("Failed to open items.txt\n");
        return 0;
    }

    int i = 0;
    while (!feof(fp) && i < MAX_ITEMS) {
        int id, quantity;
        char name[MAX_NAME_LEN];
        fscanf(fp, "%d %s %d", &id, name, &quantity);
        items[i].id = id;
        strcpy(items[i].name, name);
        items[i].quantity = quantity;
        i++;
    }

    fclose(fp);
    return i;
}

void write_items(Item items[], int num_items) {
    FILE *fp;
    fp = fopen("items.txt", "w");
    if (fp == NULL) {
        printf("Failed to open items.txt\n");
        return;
    }

    for (int i = 0; i < num_items; i++) {
        fprintf(fp, "%d %s %d\n", items[i].id, items[i].name, items[i].quantity);
    }

    fclose(fp);
}

void print_items(Item items[], int num_items) {
    printf("ID\tName\tQuantity\n");
    for (int i = 0; i < num_items; i++) {
        printf("%d\t%s\t%d\n", items[i].id, items[i].name, items[i].quantity);
    }
}

int main() {
    Item items[MAX_ITEMS];
    int num_items = read_items(items);

    while (1) {
        printf("1. Add item\n");
        printf("2. Remove item\n");
        printf("3. Update quantity\n");
        printf("4. Print items\n");
        printf("5. Exit\n");
        printf("Enter your choice: ");

        int choice;
        scanf("%d", &choice);

        switch (choice) {
            case 1: {
                if (num_items == MAX_ITEMS) {
                    printf("Maximum number of items reached\n");
                } else {
                    Item item;
                    printf("Enter item ID: ");
                    scanf("%d", &item.id);
                    printf("Enter item name: ");
                    scanf("%s", item.name);
                    printf("Enter item quantity: ");
                    scanf("%d", &item.quantity);
                    items[num_items] = item;
                    num_items++;
                    write_items(items, num_items);
                    printf("Item added successfully\n");
                }
                break;
            }
            case 2: {
                int id;
                printf("Enter item ID to remove: ");
                scanf("%d", &id);
                int found = 0;
                for (int i = 0; i < num_items; i++) {
                    if (items[i].id == id) {
                        for (int j = i; j < num_items - 1; j++) {
                            items[j] = items[j + 1];
                        }
                        num_items--;
                        write_items(items, num_items);
                        printf("Item removed successfully\n");
                        found = 1;
                        break;
                    }
                }
                if (!found) {
                    printf("Item not found\n");
                }
                break;
            }
            case 3: {
                int id, quantity;
                printf("Enter item ID to update quantity: ");
                scanf("%d", &id);
                int found = 0;
                for (int i = 0; i < num_items; i++) {
                    if (items[i].id == id) {
                        printf("Enter new quantity: ");
                        scanf("%d", &quantity);
                        items[i].quantity = quantity;
                        write_items(items, num_items);
                        printf("Quantity updated successfully\n");
                        found = 1;
                        break;
                    }
                }
                if (!found) {
                    printf("Item not found\n");
                }
                break;
            }
            case 4: {
                print_items(items, num_items);
                break;
            }
            case 5: {
                printf("Exiting...\n");
                return 0;
            }
            default: {
                printf("Invalid choice\n");
                break;
            }
        }
    }

    return 0;
}

这个程序使用了一个`Item`结构体来存储每个商品的ID、名称和数量。它从文本文件`items.txt`中读取商品信息，并在修改后将其写回文件。可以通过菜单实现添加、删除、更新和打印商品的功能。