C++发票程序问题：customerInvoice函数失效及老年折扣需求

我正在收尾C++发票程序，尝试让customerInvoice函数正常输出，但调用该函数时出现错误，无法显示函数内的发票内容，其他变量输入均正常。同时需要实现老年折扣功能：当客户年龄≥60岁时，可享受购买金额5%的折扣。

原代码 #

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

const float flatTaxRate = 0.08;
const float seniorDiscountRate = 0.05;

int getIntValue (string toInput){
    cout << "Please enter " << toInput <<": ";
    int value;
    cin >> value;
    return value;
}

string choiceOfItem(int choice) {
    return choice == 1 ? "Bread" :
           choice == 2 ? "Milk" :
           choice == 3 ? "Soap" :
           choice == 4 ? "Eggs" :
           choice == 5 ? "Deodorant" :
           choice == 6 ? "Juice" :
           choice == 7 ? "Chips" :
           choice == 8 ? "Forks" :
           choice == 9 ? "Spoons" :
           choice == 10 ? "Cups" :
    "Invalid Item: Select Again";
}

int getIntInputValues (string toInput){
    cout << "Please enter " << toInput <<": ";
    int value;
    cin >> value;
    return value;
}

double getDoubleInputValues (string toInput){
    cout << "Please enter " << toInput <<": ";
    double value;
    cin >> value;
    return value;
}

bool customerAge(int age){
    const int seniorCustomer = 60;
    return age >= seniorCustomer;
}

void customerInvoice(int choice, double price, int age)
{
    cout << "-----------------------------------
";
    cout << "
" << "Invoice" << "
";
    //can use \n as a tab
    
    if(seniorCustomer(age))
    {
        price -= price * seniorDiscountRate;
    }
     
    cout << choiceOfItem(choice) <<":" << "
" <<"$"<< price << endl;
    cout << "Tax:" << "
" <<"$"<< price * flatTaxRate << endl;
    cout << "Discount:" << "
" <<"$"<< "-" << price * seniorDiscountRate << endl;
    cout << "Total:" << "
"<< "$" << price + (price * flatTaxRate) << endl;
    cout << "-----------------------------------
";
}

int main()
{
    const int MIN_VALID = 1;
    const int MAX_VALID = 10;

    cout << "What would you like to buy?" << endl;
    
    for (int choice = MIN_VALID; choice <=MAX_VALID; ++choice)
    {
        cout << choice << ". " << choiceOfItem(choice)<< endl;
    }
    cout << endl;    

    int choice = getIntValue("your choice");

   
    while (choice < MIN_VALID || choice > MAX_VALID)
    {
        cout << "Sorry, " << choice << " wasn't a valid choice" << endl;
        cout << "Please try again:" << endl;
        choice = getIntValue("your choice");
    }
    
    double price = getDoubleInputValues("price");

    
    int age = getIntInputValues("age");

       
    bool seniorCustomer;
       
    cout << " " << endl;
        
    customerInvoice;
    
    cout << choiceOfItem(choice) << endl;
    cout << price << endl;
    cout << age << endl;
    cout << seniorCustomer;
    
    return 0;
}

核心问题修复 #

• 函数调用错误：main中仅写customerInvoice不会执行函数，必须传入参数并加括号，正确写法为customerInvoice(choice, price, age);
• 函数名误用：customerInvoice中判断老年客户的函数名应为customerAge(age)，而非seniorCustomer(age)——seniorCustomer是customerAge内部的常量，不是函数
• 折扣逻辑错误：原代码直接修改原价导致后续计算混乱，应先单独计算折扣金额，再基于原价计算税费和最终总价
• 字符串换行错误：C++不支持直接跨行写字符串，需将换行替换为\n
• 冗余变量：main中未初始化的bool seniorCustomer无实际用途，直接删除

修复后的完整代码 #

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

const float flatTaxRate = 0.08;
const float seniorDiscountRate = 0.05;

int getIntValue(string toInput) {
    cout << "Please enter " << toInput << ": ";
    int value;
    cin >> value;
    return value;
}

string choiceOfItem(int choice) {
    return choice == 1 ? "Bread" :
           choice == 2 ? "Milk" :
           choice == 3 ? "Soap" :
           choice == 4 ? "Eggs" :
           choice == 5 ? "Deodorant" :
           choice == 6 ? "Juice" :
           choice == 7 ? "Chips" :
           choice == 8 ? "Forks" :
           choice == 9 ? "Spoons" :
           choice == 10 ? "Cups" :
           "Invalid Item: Select Again";
}

// 合并重复的整数输入函数
int getIntInputValues(string toInput) {
    return getIntValue(toInput);
}

double getDoubleInputValues(string toInput) {
    cout << "Please enter " << toInput << ": ";
    double value;
    cin >> value;
    return value;
}

// 重命名函数，语义更清晰
bool isSeniorCustomer(int age) {
    const int seniorThreshold = 60;
    return age >= seniorThreshold;
}

void customerInvoice(int choice, double price, int age) {
    cout << "-----------------------------------\n";
    cout << "\nInvoice\n";
    
    double discount = 0.0;
    if (isSeniorCustomer(age)) {
        discount = price * seniorDiscountRate;
    }
    
    double tax = price * flatTaxRate;
    double total = price + tax - discount;

    // 设置金额输出格式，保留两位小数
    cout << fixed << setprecision(2);
    cout << choiceOfItem(choice) << ": $" << price << endl;
    cout << "Tax: $" << tax << endl;
    cout << "Discount: $" << discount << endl;
    cout << "Total: $" << total << endl;
    cout << "-----------------------------------\n";
}

int main() {
    const int MIN_VALID = 1;
    const int MAX_VALID = 10;

    cout << "What would you like to buy?" << endl;
    
    for (int i = MIN_VALID; i <= MAX_VALID; ++i) {
        cout << i << ". " << choiceOfItem(i) << endl;
    }
    cout << endl;    

    int choice = getIntValue("your choice");
    while (choice < MIN_VALID || choice > MAX_VALID) {
        cout << "Sorry, " << choice << " wasn't a valid choice" << endl;
        cout << "Please try again:" << endl;
        choice = getIntValue("your choice");
    }
    
    double price = getDoubleInputValues("price");
    int age = getIntInputValues("age");

    cout << endl;
    customerInvoice(choice, price, age);

    return 0;
}

额外优化说明 #

• 合并了重复的整数输入函数，减少冗余代码
• 重命名判断老年客户的函数，语义更直观
• 添加金额格式控制，确保输出保留两位小数，符合发票规范
• 调整计算逻辑，基于原价计算税费和折扣，避免数值混乱

内容的提问来源于stack exchange，提问作者Johng Jangus