如何修改收银程序代码在receipt.dat中显示所有已购商品清单？

原代码存在的核心问题 #

• 未初始化文件指针就写入：程序前半段调用fprintf(fp)时，fp还未通过fopen初始化，属于未定义行为，无法正常写入内容
• 未存储所有商品信息：仅用单个变量保存当前商品的价格和数量，未记录全部商品明细，导致收据无法列出所有已购商品
• 收据内容错误：仅输出最后一件商品的数量，且Grand total错误使用了$符号（应为RM）

修改后的完整代码 #

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

#define MAX_ITEMS 50  // 可按需调整最大商品数量

int main()
{
    float prices[MAX_ITEMS];
    int quantities[MAX_ITEMS];
    float amount = 0.0, discount = 0.0, amountToBePaid, cash, change;
    int counter = 0;
    char decision; 
    FILE *fp;
    
    printf("============\n");
    printf("Happy Market\n");
    printf("============\n\n");

    do {
        counter++;
        printf("Input item #%d price: RM ", counter);
        scanf("%f", &prices[counter-1]);
        printf("Quantity: ");
        scanf("%d", &quantities[counter-1]);
        
        amount += prices[counter-1] * quantities[counter-1];
        
        printf("Current total is RM %.2f\n", amount);
        printf("\nAdd another item? (Y/N) :");
        scanf(" %c", &decision);
    } while (decision == 'Y' || decision == 'y');

    // 计算折扣
    if(amount <= 100)
    {
        discount = (amount * 10) / 100;
        printf("\nTotal discount: RM%.2f", discount);
        printf("\nDiscount eligible is 10 percent");
    }
    else if(amount > 100 && amount < 200)
    {
        discount = (amount * 15) / 100;
        printf("\nTotal discount: RM%.2f", discount);
        printf("\nDiscount eligible is 15 percent");
    }
    else if(amount >= 200 && amount < 300)
    {
        discount = (amount * 20) / 100;
        printf("\nTotal discount: RM%.2f", discount);
        printf("\nDiscount eligible is 20 percent");
    }
    else if(amount >= 300)
    {
        discount = (amount * 25) / 100;
        printf("\nTotal discount: RM%.2f", discount);
        printf("\nDiscount eligible is 25 percent");
    }
    
    amountToBePaid = amount - discount;

    printf("\n*******************************");
    printf("\nItem(s) sub total: RM %.2f", amount);
    printf("\n*******************************");
    printf("\n\nGrand total: RM%0.2f", amountToBePaid);
    printf("\nAmount received: RM ");
    scanf("%f", &cash);
    change = cash - amountToBePaid;
    printf("Change: RM %.2f", change);
    printf("\n\n*******************************");
    printf("\nThank you, please come again!");
    
    // 打开文件并写入收据
    fp = fopen("receipt.dat", "w");
    if(fp == NULL) {
        printf("\nError opening file!");
        return 1;
    }
    
    fprintf(fp,"*******************************\n");
    fprintf(fp,"HAPPY MARKET\n");
    fprintf(fp,"*******************************\n");
    fprintf(fp,"%-10s %-15s %-10s %-10s\n", "Item No.", "Price (RM)", "Quantity", "Subtotal");
    fprintf(fp,"-----------------------------------------\n");
    
    // 遍历写入所有商品明细
    for(int i = 0; i < counter; i++) {
        float subtotal = prices[i] * quantities[i];
        fprintf(fp,"%-10d %-15.2f %-10d %-10.2f\n", i+1, prices[i], quantities[i], subtotal);
    }
    
    fprintf(fp,"-----------------------------------------\n");
    fprintf(fp,"Sub total:\t\t RM%.2f\n", amount);
    fprintf(fp,"Discount:\t\t RM%.2f\n", discount);
    fprintf(fp,"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n");
    fprintf(fp,"Grand total:\t\t RM%.2f\n", amountToBePaid);
    fprintf(fp,"Amount received:\t RM%.2f\n", cash);
    fprintf(fp,"Change:\t\t\t RM%.2f\n", change);
    fprintf(fp,"*******************************\n");
    fprintf(fp,"Thank you, please come again!\n");
    
    fclose(fp);
    
    return 0;
}

关键修改说明 #

1. 添加商品存储结构：用两个数组prices和quantities分别保存每件商品的价格和数量，确保所有商品信息被完整记录
2. 修正文件操作逻辑：仅在需要写入收据时打开文件，同时增加文件打开失败的判断，避免程序异常
3. 生成商品明细：通过循环遍历数组，将每件商品的编号、价格、数量、小计写入收据，符合预期格式
4. 修复符号错误：把Grand total中的$改为RM，保持货币单位统一
5. 优化输入循环：改用do-while循环，避免重复编写初始商品输入代码，逻辑更简洁

内容的提问来源于stack exchange，提问作者L4Lebbit