从一个简单的超市收银系统，我们来练习一个系统如何设计，然后如何实现的思路。

在Ubuntu环境下使用C语言编写一个简单的超市收银系统。以下是一个基本的示例，涵盖了商品管理、购物车、交易处理等功能。

代码

#include <stdio.h>
#include <stdlib.h>// 商品结构体
struct Product {int id;char name[50];float price;
};// 购物车项结构体
struct ShoppingCartItem {struct Product product;int quantity;
};// 交易结构体
struct Transaction {struct ShoppingCartItem *items;int itemCount;
};// 商品管理结构体
struct Inventory {struct Product *products;int productCount;
};// 初始化商品管理系统
struct Inventory initializeInventory() {struct Inventory inventory;inventory.products = NULL;inventory.productCount = 0;return inventory;
}// 添加商品到库存
void addProduct(struct Inventory *inventory, struct Product product) {inventory->products = realloc(inventory->products, (inventory->productCount + 1) * sizeof(struct Product));inventory->products[inventory->productCount++] = product;
}// 显示库存信息
void displayInventory(struct Inventory inventory) {printf("Inventory:\n");for (int i = 0; i < inventory.productCount; ++i) {printf("%d. %s - $%.2f\n", inventory.products[i].id, inventory.products[i].name, inventory.products[i].price);}
}// 获取商品信息
struct Product getProductInfo(struct Inventory inventory, int productId) {for (int i = 0; i < inventory.productCount; ++i) {if (inventory.products[i].id == productId) {return inventory.products[i];}}struct Product notFound;notFound.id = -1;return notFound;
}// 初始化交易
struct Transaction initializeTransaction() {struct Transaction transaction;transaction.items = NULL;transaction.itemCount = 0;return transaction;
}// 添加商品到购物车
void addToCart(struct Transaction *transaction, struct Product product, int quantity) {transaction->items = realloc(transaction->items, (transaction->itemCount + 1) * sizeof(struct ShoppingCartItem));transaction->items[transaction->itemCount].product = product;transaction->items[transaction->itemCount].quantity = quantity;++transaction->itemCount;printf("Added %d %s(s) to the cart.\n", quantity, product.name);
}// 显示购物车
void displayCart(struct Transaction transaction) {float total = 0.0;printf("Shopping Cart:\n");for (int i = 0; i < transaction.itemCount; ++i) {struct ShoppingCartItem item = transaction.items[i];printf("%s - Quantity: %d\n", item.product.name, item.quantity);total += item.product.price * item.quantity;}printf("Total Price: $%.2f\n", total);
}// 完成交易
void completeTransaction(struct Transaction transaction) {printf("Transaction completed. Thank you!\n");free(transaction.items);
}int main() {struct Inventory inventory = initializeInventory();// 添加一些商品addProduct(&inventory, (struct Product){1, "Milk", 2.5});addProduct(&inventory, (struct Product){2, "Bread", 1.0});addProduct(&inventory, (struct Product){3, "Eggs", 3.0});struct Transaction transaction = initializeTransaction();// 超市收银系统while (1) {displayInventory(inventory);int productId;printf("Enter product ID to add to cart (or 0 to finish): ");scanf("%d", &productId);if (productId == 0) {break;}struct Product product = getProductInfo(inventory, productId);if (product.id != -1) {int quantity;printf("Enter quantity: ");scanf("%d", &quantity);addToCart(&transaction, product, quantity);} else {printf("Product not found.\n");}}displayCart(transaction);completeTransaction(transaction);// 释放资源free(inventory.products);return 0;
}

编译：

gcc supermarket.c -o supermarket
./supermarket

程序设计的详细过程：

步骤 1: 定义数据模型

在程序设计的起始阶段，定义了程序需要用到的数据模型，包括商品、购物车项和交易。使用结构体表示这些概念，其中包括商品（Product）、购物车项（ShoppingCartItem）和交易（Transaction）。

struct Product {int id;char name[50];float price;
};struct ShoppingCartItem {struct Product product;int quantity;
};struct Transaction {struct ShoppingCartItem *items;int itemCount;
};

步骤 2: 商品管理

设计商品管理系统，包括添加商品到库存和获取商品信息的功能。使用结构体 Inventory 来保存商品信息，并定义相应的函数。

struct Inventory {struct Product *products;int productCount;
};// 添加商品到库存
void addProduct(struct Inventory *inventory, struct Product product) {// 通过realloc动态分配内存以保存商品inventory->products = realloc(inventory->products, (inventory->productCount + 1) * sizeof(struct Product));inventory->products[inventory->productCount++] = product;
}// 获取商品信息
struct Product getProductInfo(struct Inventory inventory, int productId) {for (int i = 0; i < inventory.productCount; ++i) {if (inventory.products[i].id == productId) {return inventory.products[i];}}struct Product notFound;notFound.id = -1;return notFound;
}

步骤 3: 用户界面

设计用户界面，实现基本的用户交互，允许用户选择商品并添加到购物车。使用结构体 CashierUI 和相应的函数。

struct CashierUI {struct Inventory inventory;struct Transaction transaction;
};// 显示库存信息
void displayInventory(struct Inventory inventory) {// 输出商品列表
}// 添加商品到购物车
void addToCart(struct Transaction *transaction, struct Product product, int quantity) {// 将商品添加到购物车
}// 显示购物车信息
void displayCart(struct Transaction transaction) {// 输出购物车内容
}// 完成交易
void completeTransaction(struct Transaction transaction) {// 输出总价和完成交易信息
}

步骤 4: 交易处理

实现交易处理功能，计算购物车中商品的总价并完成交易。

// 初始化交易
struct Transaction initializeTransaction() {struct Transaction transaction;transaction.items = NULL;transaction.itemCount = 0;return transaction;
}// 完成交易
void completeTransaction(struct Transaction transaction) {// 输出总价和完成交易信息// 释放购物车内存free(transaction.items);
}

步骤 5: 主程序

在主程序中，创建超市收银系统实例，添加一些商品，然后启动收银系统。

int main() {// 初始化商品管理系统struct Inventory inventory = initializeInventory();// 添加一些商品addProduct(&inventory, (struct Product){1, "Milk", 2.5});addProduct(&inventory, (struct Product){2, "Bread", 1.0});addProduct(&inventory, (struct Product){3, "Eggs", 3.0});// 初始化交易struct Transaction transaction = initializeTransaction();// 超市收银系统while (1) {// 显示库存信息displayInventory(inventory);int productId;printf("Enter product ID to add to cart (or 0 to finish): ");scanf("%d", &productId);if (productId == 0) {break;}// 获取商品信息struct Product product = getProductInfo(inventory, productId);if (product.id != -1) {int quantity;printf("Enter quantity: ");scanf("%d", &quantity);// 添加商品到购物车addToCart(&transaction, product, quantity);} else {printf("Product not found.\n");}}// 显示购物车displayCart(transaction);// 完成交易completeTransaction(transaction);// 释放资源free(inventory.products);return 0;
}

这个设计过程包括了程序的整体结构、数据模型的定义、功能的实现以及用户界面的设计。当设计一个更大规模的系统时，可能需要考虑更多的功能，例如支付处理、库存管理、用户认证等。这个简化的例子提供了一个基本的框架，可以根据实际需求进行扩展。