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This might be a stupid question to ask but I'm curious. I decided to test this myself and I got a value of 2 for both HIGH and LOW, why would it output 2?

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In Arduino AVR Boards, HIGH and LOW are currently macros:

https://github.com/arduino/ArduinoCore-avr/blob/1.6.23/cores/arduino/Arduino.h#L40-L41

#define HIGH 0x1
#define LOW  0x0

This means that sizeof(HIGH) is equivalent to sizeof(0x1). 0x1 is an integer constant. The default type of integer constants is int. On an 8 bit microcontroller like the ATmega2560 used by your Arduino Mega, an int is 16 bits.

That is why sizeof(HIGH) returns 2 (16 bits / 8 bits/byte = 2 bytes).

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    Thanks that answers my question! – Cordell Dec 30 '18 at 5:37

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