Sololearn is a free learning app helps you to learn different programming languages starting from very basics.
I have been a part of sololearn for few weeks and equipped myself with the basics of programming language including C, C+, Java and Javascript.
If even you wish to practise some questions you can opt for sololearn.
You can also send challenges to different people connected on the sololearn platform and can judge your performance on the leaderboard.Though the content is at a superficial level yet is good for begineers. The content is also sufficient for basic knowledge but don’t expect for deep knowledge
The app is user friendly and you can have discussions with the leaderboard people