如何正确设置C ++中的双精度 [英] How to properly set precision for doubles in C++

问题描述

我正在做一个项目，我需要做一些数学，并给用户输出美元，所以我想让我的控制台告诉用户一个答案像 $ 20.15 而不是 $ 20.153 。我使用设置精度函数：
cout<< setprecision（2）; ，但不是让数字成为我想要的数字，而是转换成科学记数法。

I'm working on a project where I need to do some math and give the user output with dollars in it, so I would like to have my console tell the user an answer like $20.15 instead of $20.153. I used the set precision function as such: cout << setprecision(2);, but rather than have the numbers become what I want them to be, they are converted into scientific notation.

输出大量数字，所以拥有 setprecision 这样的函数对我来说最适合使用。

I'm outputting a lot of numbers, so having a function like setprecision would be best for me for ease of use.

如何正确地显示数字只有两个小数位，并且没有控制台给我科学记数法的数字？

How do I properly have the numbers displayed with only two decimal places and not have the console give me numbers in scientific notation?

感谢

Nathan

编辑：

这是我的代码的一部分I' m有问题：

Here is the part of my code I'm having problems with:

int main() {

cout << setprecision(2);

if (totalCostHybrid < totalCostNonHybrid) {
            cout << "Hybrid car: " << endl;
            cout << "Total cost: " << totalCostHybrid << endl;
            cout << "Total gallons used: " << milesPerYear / hybridEffic << endl;
            cout << "Total gas cost: " << gasCostHybrid << endl;
            cout << "Non-hybrid car: " << endl;
            cout << "Total cost: " << totalCostNonHybrid << endl;
            cout << "Total gallons used: " << milesPerYear / nonHybridEffic << endl;
            cout << "Total gas cost: " << gasCostNonHybrid << endl;
            cout << "Hybrid is cheaper!" << endl;
}

显然有更多的东西，但这是我需要帮助。 / p>

Obviously there's more to it, but this is what I need help with.

推荐答案

要解决这个问题，你应该使用cout的固定浮点表示法。您可以在此处找到更多信息。

To fix that, you should use fixed floating-point notation for cout. You can find more info here.

尝试addind cout<<固定到您的代码，如下面的代码。要将精度设置为 2 ，可以使用 precision 属性。

Try addind cout << fixed to your code, like the code below. To set the precision to 2, you can use the precision property.

cout << fixed;
cout.precision(2);

以下是完整的代码：

using namespace std;

int main() {

    cout << fixed;
    cout.precision(2);

    if (totalCostHybrid < totalCostNonHybrid) {
            cout << "Hybrid car: " << endl;
            cout << "Total cost: " << totalCostHybrid << endl;
            cout << "Total gallons used: " << milesPerYear / hybridEffic << endl;
            cout << "Total gas cost: " << gasCostHybrid << endl;
            cout << "Non-hybrid car: " << endl;
            cout << "Total cost: " << totalCostNonHybrid << endl;
            cout << "Total gallons used: " << milesPerYear / nonHybridEffic << endl;
            cout << "Total gas cost: " << gasCostNonHybrid << endl;
            cout << "Hybrid is cheaper!" << endl;
     }
}

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