C language question

Question

For my practice i took a calculator app for practice where in if statement there is DBX max what does it do and how it came. I Googled but it didnt worked.. Line 31
https://sololearn.com/compiler-playground/cVgx4GezkW19/?ref=app

Answer 1

DBL_MAX is the maximum float that can be represented. As I understand your code, it seems you want to use DBL_MAX to indicate an invalid result due to inappropriate user input?

Answer 2

Lisa is DBL_MAX is an keywords?

Answer 3

It is a constant.