why in the cycle for (double i=-1; i<=1; i=i+0.1) the 0 is equal -1.38778e-016

for(double i=-1; i<=1;i=i+0.1)

cout<<i<<"\n";

result:

-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
-1.38778e-016
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1