На стеке объяснили по подробнее, теперь понял)
'0' is just the human readable represetation of the integer 48 which is considered as code for the character '0' in ASCII.
ASCII digit codes:
When you add 4 to 48 which is integer representation of '0' you are getting 52.
When you write it it to the screen then the character represented by its code is being displaed (in this case '4')
