Why is this happening?

Question

#include<iostream>
#include<conio.h>

using namespace std;

int main(){

int n;
double x=87.19856;

float y=87.19856;

n=x;
cout<<endl<<"x= "<<x-n;
//in this case x=0.19856

n=y;

cout<<endl<<"y= "<<y-n;
//in this case y=0.198563 the number "3" is wrong.
return 0;

}
/* this happen with others numbers too. my english is pretty bad*/

Answer 1

http://effbot.org/pyfaq/why-are-floating-point-calculations-so-inaccurate.htm

tl;dr - There is no guarantee for computers to represent floating-point values accurately.

Answer 2

woooo "Some decimal numbers can’t be represented exactly in binary, resulting in small roundoff errors." and "double has more precision than floats."
I didn't have idea. thanks for the link and the answer.