I can't understand why not equal

Question

in this code,
why (x!=0.3) and (y!=0.6) ?

#include <iostream>
using namespace std;

int main() {
float x;
double y;

x = 0.1+0.1+0.1;
y = 0.2+0.2+0.2;

if (x==0.3)
cout << "true \n";
else
cout << "false \n";

if (y==0.6)
cout << 1 << endl;
else
cout << 0 << endl;

return 0;
}

Answer 1

It's related on how float and double are written by the computer. It's first converted to binary and then translated on a power of 2.
As it's stocked on minimum 4 (8 for double) bytes and not an infinity, there is a little difference on the real value and the approximated one (in power of 2). It can accumulate quite quickly with operations.
That's why :

#include <iostream>
using namespace std;

int main() {
cout << 0.3 - 0.1 - 0.1 - 0.1 << endl;
return 0;
}

will output :
-2.7756e-17

Answer 2

more info here :
https://en.m.wikipedia.org/wiki/Floating_point

Answer 3

Thanks Dorian, I understood it.