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How to prevent rounding error in C ++?

How can I prevent a rounding error in C ++ or fix it?

Example:

float SomeNumber = 999.9999;
cout << SomeNumber << endl;

He prints 1000!

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4 answers

You can change the rounding done by coutsetting the precision.

cout.precision(7);
float SomeNumber  = 999.9999;
cout << SomeNumber  << endl;

Alternatively you can use printffrom cstdio.

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By default, formatted output std::ostreamrounds off floating point values ​​to six significant decimal digits. You need seven to avoid rounding your number to 1000:

cout << setprecision(7) << SomeNumber << endl;
        ^^^^^^^^^^^^^^^

, , float, 32- IEEE. , double. , 1000, , :

float SomeNumber = 999.99999; // 8 significant figures
cout << setprecision(10) << SomeNumber << endl;
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, setprecision iomanip.

float SomeNumber = 999.9999;
std::cout << SomeNumber << std::endl; //outputs 1000
std::cout << std::setprecision (7) << SomeNumber << std::endl; //outputs 999.9999
return 0;

, SomeNumber, 999.9999, ( , float).

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, cout, .precision. , :

You cannot avoid such rounding errors using floating point numbers. You need to present your data in a different way. For example, if you want 5 digits of precision, just save it as a long one that represents the number of your smallest units.

those. 5.23524 with an accuracy of 0.00001 can be represented as long (or int, if your range of values ​​is suitable) as 523524. You know that the units are 0.00001, so you can easily make it work.

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