Didnt get whats wrong with using _ ?
Thereisnothingwrongwithusingunderscores. The problem is writing code without white space. The compiler doesn't care, but you didn't ask the compiler what was wrong with your code. You asked people, and people DO care about white space.
For loop is fast but you didnt noticed delay()
Saw it. Thought it stupid. There is NO guarantee that sticking your head in the sand for ANY length of time will make another byte arrive on the serial port.
My array is not const how to use with memcmp?
Understand what const means there. It means that memcmp() will not alter the input data in any way. It does NOT mean that the array must be const.