If you've seen "CS 1.8" online, it's likely a , a pirated repack, or malware disguised as a game. Downloading such files is risky (viruses, spyware).
I notice you're asking about — but that version doesn't officially exist. The last major retail version of classic CS is Counter-Strike 1.6 , followed by Condition Zero and then Source. counter strike 1.8 download pc