[英]How to properly set precision for doubles in C++
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
. 我正在做一个项目,我需要做一些数学运算,并在其中提供带美元的用户输出,因此我想让控制台告诉用户一个像$20.15
而不是$20.153
。 I used the set precision function as such: cout << setprecision(2);
我这样使用了set precision函数: cout << setprecision(2);
, but rather than have the numbers become what I want them to be, they are converted into scientific notation. ,而不是让数字变成我想要的数字,而是将其转换为科学计数法。
I'm outputting a lot of numbers, so having a function like setprecision
would be best for me for ease of use. 我输出了很多数字,因此对于我来说,使用setprecision
类的功能对我来说是最好的。
How do I properly have the numbers displayed with only two decimal places and not have the console give me numbers in scientific notation? 如何正确显示仅用小数点后两位数字显示的数字,而不使控制台以科学计数形式显示数字?
Thanks 谢谢
Nathan 弥敦道
EDIT: 编辑:
Here is the part of my code I'm having problems with: 这是我遇到问题的部分代码:
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;
}
Obviously there's more to it, but this is what I need help with. 显然还有更多,但这是我需要帮助的。
Iostreams are a pain for formatting floating-point values. Iostream是格式化浮点值的痛苦。 But why are you using floating-point to represent currency values? 但是,为什么要使用浮点数来表示货币值? You should store integer pennies (or tenth-pennies) because, though you're not measuring in whole numbers of dollars, your values are actually fixed-point. 您应该存储整数美分(或十分之一美分),因为尽管您没有用整数来衡量,但您的值实际上是定点的。 And you really don't need the trouble that floating-point brings. 您真的不需要浮点运算带来的麻烦。 And then you can stream the whole and "fractional" parts of your value separately (use /
and %
!), as integers, with a '.'
然后,您可以分别将值的整个和“小数”部分(使用/
和%
!)以整数形式用'.'
in the middle. 在中间。
In the meantime, try std::fixed
. 同时,尝试使用std::fixed
。
To fix that, you should use fixed floating-point notation for cout. 要解决此问题,您应该对cout使用固定的浮点符号。 You can find more info here . 您可以在此处找到更多信息。
Try addind cout << fixed
to your code, like the code below. 尝试将addind cout << fixed
到您的代码,例如下面的代码。 To set the precision to 2
, you can use the precision
property. 要将precision设置为2
,可以使用precision
属性。
cout << fixed;
cout.precision(2);
Here is the complete code: 这是完整的代码:
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;
}
}
Cheat and watch purists go crazy... 作弊和看纯粹主义者发疯...
double time; //Only want two decimal places.
double timeCon = time * 100.0; //Pull out the two decimals I want.
int timeCut = timeCon; //Cut all decimal values.
double timeRevert = timeCut / 100.0; //Laugh.
cout << timeRevert << endl; //Watch heads explode.
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