Once programming

Question

I always had question that how can i programming once for several platform(Devices)?

i know that some language like QT can do it but
screen size or some functionality of devises
may not be same

Answer 1

If it’s game, you can use a game engine. Most programming languages also have a library that takes care of lower level stuff for you (just look for it on google)

Answer 2

thanks for answer
that is right...
but i have chat app like whats up or telegram that have website and pc and android ... versions