does adding 1 in my code doesn't make any change??

[vkash]

#include<iostream>
using namespace std;
int main()
{
    using namespace std;
    float a=2e+6;
    cout<<a<<endl;
    float b=a+1;
    cout<<b<<endl;
    cout<<b-a<<endl;
    return 0;
}

output is a shown in attachment..
if b and a are same then why their subtraction gives 1??
however i have assigned b=a+1.. if it is so then why both are shown same??