Double vs float precision issue

Question

#include <iostream>

int main()
{
    double a = 2 , b = 3;

    double answer = a/b;
    std::cout << answer;
    std::cout << std::to_string(answer);
}

Float or double I get : 0.666667;

I was expected more precision from the double ; How do i get something more like : 0.666666666666667

Edit : and i need to not lose the precision by using to_string;

Your stream controls what precision is displayed. [http://www.cplusplus.com/reference/iomanip/setprecision/](http://www.cplusplus.com/reference/iomanip/setprecision/) — drescherjm, Jul 14 '20 at 02:03
Related to the new question: [https://stackoverflow.com/questions/16605967/set-precision-of-stdto-string-when-converting-floating-point-values](https://stackoverflow.com/questions/16605967/set-precision-of-stdto-string-when-converting-floating-point-values) — drescherjm, Jul 14 '20 at 02:23

score 2 · Answer 1 · answered Jul 14 '20 at 02:06

2

I was expected more precision from the double

The precision of a floating point type is separate concept from the precision of a decimal number in textual representation.

You didn't specify the precision that you want, so default was used. It just so happens that the default isn't what you arbitrarily expected. You can specify the precision for example like this:

std::cout.precision(15);

answered Jul 14 '20 at 02:06

eerorika

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thanks , but if i need to use to_string on it it get back to de last precision std::cout << std::to_string(buff) << "\n"; – Jonathan Layduhur Jul 14 '20 at 02:14

Geno C · Answer 2 · 2020-07-14T02:15:21.870

0

The setprecision is in the header file #include<iomanip> which will let you set the decimal precision.

For example:

#include <iostream>
#include <iomanip>  // The precision manipulator is in this header file 

int main()
{
    double a = 2 , b = 3;

    double answer = a/b;
    std::cout << std::setprecision(15) << answer;
    return 0;
}

edited Jul 14 '20 at 02:15

answered Jul 14 '20 at 02:10

Geno C

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Double vs float precision issue

2 Answers2