I new at programming ATmega with C++ what is the process( steps ) of doing the function below?

[code builder]

programming ATmega with C++ what is the process of doing the function below?
EXAMPLES

Assuming that the Open USB board portb LED's display 11 in binary then:
The command line " 1 3" should produce the values
12
13
14
i.e. increment of one, three times.

Assuming that the Open USB board portb LED's display 100 in binary then:
The command line "2 4" should produce the values
98
96
94
92
i.e. decrement of two, four times.

Assuming that the Open USB board portb LED's display 252 in binary then:
The command line " 3 3" should produce the values
255
2
5
make sure you understand how this is derived. See the section on "wrapping around".


Assuming that the Open USB board portb LED's display 13 in binary then:
The command line " -10 3" should produce the values
3
249
239