We usually use<iostream. h>

Question

I don't know why so!
Here it's working without <. h>

Answer 1

Maybe for the fact that it's for compiling code in non-standard old turbo c++ compiler?
Sololearn compiler uses <iostream> which is used by modern day compilers.

check the SO link for difference between them
https://stackoverflow.com/questions/2976477/difference-between-iostream-and-iostream-h

Read the below post on why to avoid it(turbo compiler) when possible...
https://www.sololearn.com/discuss/288609/?ref=app