Negative lookarounds are usually what you're after:
Negative Lookbehind
-
(?<!status )code
matches code not preceded by status
-
(?<!status )(?<!post)code
matches code not preceded by status or by post
Negative Lookahead
-
code(?!smith)
matches code not followed by smith
-
code(?!smith)(?!d)
matches code not followed by smith or by d
Negated Character Classes
But to not-match just a single character you can do it with character a class:
-
code[^d]
matches code but not coded
-
code=[^0-9]
matches code=X where X is not a digit
