Why the output is 9? And runs only one time !

Question

I really don't understand why output came this this !
https://code.sololearn.com/c7AoY6Cp9t1C/?ref=app

Answer 1

So first the size of char.
You can check this by using sizeof(char), it shown 1 byte.
1 byte consist of 8bit and max value of 8 bit is 11111111 which 255.

So here you already assign c to its max value, so what happen. It'll overflow and start again from its minimum value which is 0.
You can imagine 255 in place of -1 here, just right before 0.
So 255+10 is kinda same as (-1)+10 = 9