Float in C, is 0.41 really 0.40999?

Question

C++ / C#

int main(void) {
    float x = 0.41;
    printf("%.50f",x);
}

and see

0.40999999642372131347656250000000000000000000000000

I can't understand why. Any experts on C? Tell pliz.

Answer 1

0.41 cannot be exactly represented as a sum of binary digits N1*(1/2)+N2*(1/4)+N3*(1/8)+... Only with some limited precision. Just as the number 1/3 cannot be represented as a finite decimal fraction.

Answer 2

The number is stored in binary form. Read the wiki to get started.