I've been learning C++ recently, with the endgame to be able to program the Microchip PIC18 series chips which are optimized for C language, as well as Arduino/Teensy.
This place
SoloLearn has been decent, it's free for the program, but you have to pay for the homework

. I ended up paying the $12 for a month because it's pretty cheap as far as education goes, and handy to have a built in page to test your code attempts, but if you don't want to spend a dime you can also practice C++ with this online "sandbox" for free, no account BS:
https://codehs.com/editor/explore_demo_in_sandbox/2673672Also this Ausie "Creel" has a nice, unobtuse way of explaining the concepts, in a series of ~20 minute presentations:
https://www.youtube.com/playlist?list=PL0C5825724605DB2AAlso looks to have a series on assembly language.
Edit: Steer clear of the comments section at Sololearn, unless you are desperate. The blind leading the blind.