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I am in need of a sentinel value to use to assign to a double variable initially. 0 or -1 won't work because these values are valid values in my computation and I need a value that will stand out.

Possible choices are:

  1. Maximum double value
  2. Minimum double value
  3. NAN (I would also need a method to check is_nan as well)

How can I accomplish this in the Arduino language?

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This is a matter of personal preference. I like NAN because it is almost always obvious it cannot be a valid value.

You can test for the value being NAN with isnan().

  • Right but do they exist in arduino language? The constant NAN and isnan() function (in standard c++ it's a std:: library function) – James Wierzba Apr 30 '16 at 3:22
  • The link I provided is to the doc of the avr-libc. You can use NAN and isnan() with no prefix on any AVR-based Arduino. No need to explicitly include <math.h>, as the Arduino IDE does that for you (via <Arduino.h>). I do not know about the ARM-based Arduinos (e.g., the Due). – Edgar Bonet Apr 30 '16 at 10:52

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