使用相同浮点常量值的不同模式会导致不同的结果[重复]

Question

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• floating point operations in go 2 answers

in the following snippet of go code I struggle to understand why the results are different:

func main() {
    a := -0.2; b := -0.1; 
    fmt.Println(a+b)
    //Outputs expected float value with rounding error  : -0.30000000000000004
    c := (-0.2)+(-0.1)
    fmt.Println(c)
    //Will ouput -0.3 (the actual exact constant).
}

What is happening exactly, does go somehow performs the c operation as constant instead of float64 operation when these constants are not used to instantiate floats? Full working version : https://play.golang.org/p/kUICDGFiMvf

Any insights would be appreciated, thanks.

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Answer 1

i try to use java and the resule is

public class StringTest {
    public static void main(String[] args) {

        double a = -0.2;
        double b = -0.1;
        System.out.println(a + b);
       //  -0.30000000000000004

        double c = a + b;
        System.out.println(c);
      // -0.30000000000000004

    }
}

it seems that the any programming language that uses binary floating point numbers will have this problem. some language's Number type used IEEE754 standard to represent number. And what is IEEE-745 float ,you can see it.