c++ - 在 C++ 中乘法变量有问题。 (除非硬编码，否则 C++ 不想将它们相乘)

Question

我最近选择了 cpp，并一直在做几个非常小的项目来熟悉这门语言，但我遇到了一个无论在网上哪里都无法弄清楚的困境。

#include <iostream>
using namespace std;

int main(){
    double salesTax = 0.875, gross = 0, tax = (gross*salesTax), total = (salesTax + gross); //Variables 

    cout << "Welome to StoreMart!" << endl;

    cout << "How much is your total? "; //asks user for an amount of money spent (not including tax).
    cin >> gross; //saves total spent in the gross variable

    cout << "\n\nThat brings your total with tax to $" << total << "." << endl; //prints the users total with tax.

    cout << "Price: " << gross << "$ \n\nSales Tax: $" << tax << " @" <<
        salesTax << "% \n\nTotal: $" << total << endl; //prints out something similar to the receipts you get at Wal-Mart.

    return 0;
}

如您所知，我正在构建一个小型收银机类型的程序，但问题是无论何时运行，我都只会得到如下所示的输出。

http://imgur.com/7ndthUX (无法上传图片直到 10 分所以希望 imgur 没问题:))

如有任何帮助，我们将不胜感激(如果我的数学有问题，请不要介意我对让我的程序正确运行比让数学变得完美更感兴趣。)

Answer 1

您正在根据初始值 0 计算所有依赖于 gross 的值。获取 gross 输入，然后然后计算税金和总计，在输出之前。

其他一些修复:

• 8.75% 的销售税为 0.0875
• 您只添加了销售税百分比，而不是计算值
• 您想将最终总计显示到小数点后两位

我在下面添加了修复。

#include <iostream>
using namespace std;

int main(){
    double salesTax = 0.0875;
    double gross = 0;
    double tax = 0;
    double total = 0; //Variables with initial values

    cout << "Welome to StoreMart!" << endl;

    cout << "How much is your total? "; //asks user for an amount of money spent (not including tax).
    cin >> gross; //saves total spent in the gross variable
    tax = (gross*salesTax); //calculate tax
    total = (tax + gross); //calculate total

    cout.precision(2);
    cout << "\n\nThat brings your total with tax to $" << total << "." << endl; //prints the users total with tax.

    cout << "Price: " << gross << "$ \n\nSales Tax: $" << tax << " @" <<
        salesTax*100 << "% \n\nTotal: $" << fixed << total << endl; //prints out something similar to the receipts you get at Wal-Mart.

    return 0;