The value returned by the 'Esc' key

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In the statement:
 while((ch = getch) =! ZERO)
I would like to change the value ZERO to the value returned by the
'Esc' key, but I don't know how Linux maps the keys on the key words,
as you know conio.h has a macro value for each of the function keys as
well as other keys. Is there something similar in g++? can you know of
a place in the internet that might have any info. about this topic?

T.I.A.