Why do I have to use "iostream" here instead of "stdio.h" ?

Question

I have very little experience of using codeblocks before sololearn. I used "stdio.h" as the header there but in sololearn it doesn't work! I have to use "iostream"!
Why is this happening? Can anybody explain?

Answer 1

iostream is for C++.
stdio.h is for C though it still works in C++...

You just gotta use stdio and not stdio.h

Answer 2

But stdio.h doesn't seem to be working in C++!