strcmp works sometime, but not always & blocks output to screen

[2kaud]

gets() has been removed from the standard. use gets_s() instead. As this is C++, why not use std::string?

You have a 'typo':

strcpy(second, word3);
strcpy(second, word2);

Can you spot it?

strcpy(second, word3);
strcpy(first, word2);

The reason you're currently getting different output on different systems in that in the failure case, first doesn't have anything copied into it and hasn't been initialised. Hence cout << first will display whatever happens to be in memory at the location pointed to by first. Variables should always be initialised:

	char word1[20] {};
	char word2[20] {};
	char word3[20] {};
	char first[20] {};
	char second[20] {};
	char third[20] {};