如何在 C++ 中使用 switch 语句显示价格差异

Question

对于一个课堂项目，我必须开发一个程序来计算移动设备服务的成本。用户可以选择 3 个包。服务的成本由基本价格和要使用的消息单元数决定。在用户选择一个包后，我必须让他们知道包的价格，并让他们知道其他包是否更便宜，并通过使用 switch 语句显示价格差异。我已经写了一些比较这些包的 switch 语句，但是如果有一个比所选包更便宜的包，我如何显示和计算它们会节省多少？我也是初学者，请放心。

int main() {
    bool finished = false;

    do {
        // to keep it simple
        double choice_a = 9.95;
        double choice_b = 19.95;
        double choice_c = 39.95;
        char choice;
        int message_units;
        double price;
        bool selected = false;
        // this loop shows the options initially
        do {
            cout << "Which package do you choose (enter A, B or C)" << endl;
            // you will need to check this
            cin >> choice;
            // keeping it simple
            if (choice == 'A') { price = choice_a; selected = true; }
            else if (choice == 'B') { price = choice_b; selected = true; }
            else if (choice == 'C') { price = choice_c; selected = true; }
            cout << endl;
        }
        // loops until something was selected
        while (selected == false);

        // user enters how many units is wanted
        cout << "How many message units (enter 1 - 672)" << endl;
        // again check this (if homework requires checking input)
        cin >> message_units;

        // Calculating message units
        if(message_units > 5){
            price += 100 * (message_units - 5);
        }
        if(message_units > 15){
            price += 50 * (message_units - 15);
        }

        // Total Price Output
        cout << "Your total cost is " << price/100 << endl

        // Is user done?
        char done;
        cout << "Do you want to enter another? press enter to continue.
        cin >> done;

        // check
        if (done != ' ') {
            finished = true;
        }
    }
    while (finished = false);
}

switch (choice)
{
    case 'A':
    if(choice_b < choice_a);
    cout << "You can save by switching to package B" << endl;
    else if(choice_c < choice_a);
    cout << "You can save by switching to package C" << endl;
    break;
    case 'B':
    if(choice_a < choice_b);
    cout << "You can save by switching to package A" << endl;
    else if(choice_c < choice_b);
    cout << "You can save by switching to package C" << endl;
    break;
    case 'C':
    if(choice_a < choice_c);
    cout << "You can save by switching to package A" << endl;
    else if(choice_b < choice_c);
    cout << "You can save by switching to package B" << endl;
    break;
}

Answer 1

 #include <iostream>

 using namespace std;

 int main() {
    bool finished = false;
    char choice;
    double choice_a = 9.95;
    double choice_b = 19.95;
    double choice_c = 39.95;
    int message_units;
    double price;
    bool selected = false;

    do {
        // to keep it simple
        // this loop shows the options initially
        do {
            cout << "Which package do you choose (enter A, B or C)" << endl;
            // you will need to check this
            cin >> choice;
            // keeping it simple
            if (choice == 'A') { price = choice_a; selected = true; }
            else if (choice == 'B') { price = choice_b; selected = true; }
            else if (choice == 'C') { price = choice_c; selected = true; }
            cout << endl;
        }
        // loops until something was selected
        while (selected == false);

        // user enters how many units is wanted
        cout << "How many message units (enter 1 - 672)" << endl;
        // again check this (if homework requires checking input)
        cin >> message_units;

        // Calculating message units
        if(message_units > 5){
            price += 100 * (message_units - 5);
        }
        if(message_units > 15){
            price += 50 * (message_units - 15);
        }

        // Total Price Output
        cout << "Your total cost is " << price/100 << endl;

         switch (choice)
         {
         case 'A':
         if(choice_b < choice_a)
         cout << "you can save by switching to package B it saves: " << choice_a - choice_b << " if you choose B" << endl;
         else if(choice_c < choice_a)
         cout << "You can save by switching to package C is saves: " << choice_a - choice_c << endl;
         break;
         case 'B':
         if(choice_a < choice_b)
         cout << "you can save by switching to package A it saves: " << choice_b - choice_a << " if you choose a" << endl;
         else if(choice_c < choice_b)
         cout << "you can save by switching to package C it saves: " << choice_b - choice_c << " if you choose c" << endl;
         break;
         case 'C':
         if(choice_a < choice_c)
         cout << "you can save by switching to package A it saves: " << choice_c - choice_a << " if you choose a" << endl;
         else if(choice_b < choice_c)
         cout << "you can save by switching to package A it saves: " << choice_c - choice_b << " if you choose b" << endl;
         break;
         }

        // Is user done?
        char done;
        cout << "Do you want to enter another? press enter to continue.";
        cin >> done;

        // check
        if (done != ' ') {
            finished = true;
        }

    }
    while (finished == false);


}

很抱歉没有解释，但我会尽力解释 根据您的代码。我修复了一些错误的语法并尝试匹配问题 你已经发布了，所以我定义了你在第一个之外创建的所有变量 外部 bool 以便 switch 语句可以工作，我在 switch 语句中编辑一些代码来计算节省的数量并根据条件显示它们，对不起英语不好。

Answer 2

假设您正在比较相同数量的两者，

储蓄= [（选择价格）-（更便宜的期权价格）]×数量

如果您进行此计算并将其分配给名为 Savings 的双精度类型，则可以将其打印出来。

cout

对每个 if 语句执行此操作很简单，但当然还有更好的方法来执行此操作。例如调用一个函数来为两个选项进行这个简单的计算。

编辑 1：为糟糕的格式道歉，这是在我的手机上。

编辑 2：还注意到您的控制循环语法不正确。这是一个很好的资源here

编辑 3：实际上还有许多其他问题，包括您的 switch 语句在 main 之外。

实际上，这条线没有意义。

// 计算消息单位 if(message_units > 5){ price += 100 * (message_units - 5); } if(message_units > 15){ 价格 += 50 * (message_units - 15); }

建议不要用具有不同含义的值覆盖变量。这令人困惑。最初，价格似乎是每数量的价格。然后看起来您尝试将总成本分配给它。

（我假设；它实际上并没有这样做。相反，它会将除前 5 个之外的每个单位的价格添加到您在顶部声明的单个单位价格中。对于大于 15 的块也是如此。 )

编辑 4：cmets 中的每个请求：

如果我认为您正在尝试做的事情是正确的，请替换此块：

// Calculating message units
    if(message_units > 5){
        price += 100 * (message_units - 5);
    }
    if(message_units > 15){
        price += 50 * (message_units - 15);
    }

与：

double Total_Cost;
if(message_units => 5 && message_units<15){
    Total_Cost = price * (message_units - 5);
}
else if(message_units => 15){
    Total_Cost = price * (message_units - 15);
}
else{
    Total_Cost = price * message_units;
}

即“如果您批量购买，您将免费获得前 5 个（或 15 个）”。否则，它只是价格乘以单位数量。这似乎有点奇怪，但这就是它的作用。