Object Orientation on the photon/P0?

[ScruffR]

The symptoms you are describing there are not uncommon with Dev.
It behaves somewhat counterintuitive.

• make sure you save all your files before building (no cyan dots in the file tabs left)
• don't only push the build and flash button but first the build button and only then the flash (lightning bolt) button - or remove any present .bin files in your project folder
• make sure you got the project folder selected and not just a project file as only the folder will be built. The selected file will only be edited in Dev.
• make sure you selected the correct target device

Other members could be helped when they provided a screenshot of their Dev window to spot other issues.

In your code is one puzzling line

  bool checkRead*long previousMillis, int interval)         

You should also do your millis() checks slightly different
See here

Millis() and rollover tutorial

The millis() function is handy for timing things with the Particle Photon (and Electron, and Core). It executes very quickly and has a good resolution (milliseconds). From the manual: Returns the number of milliseconds since the device began running the current program. This number will overflow (go back to zero), after approximately 49 days. Note: The return value for millis is an unsigned long, errors may be generated if a programmer tries to do math with other datatypes such as ints. Now…