CrackMe #1 :: C++ :: Difficulty : 1

KeyGenMe Location : CrackMe #1 @ Crackmes.de
Solution Location : Solution by DoomsDay

So, here is my first CrackMe. It's coded in ANSI C++. Features :
(*) NOT Packed
(*) NOT Encrypted
(*) Nice Konsole look with Double Sided Arrow Animation.

The Rules :
(*) NO Patching
(*) NO Brute-forcing

The Tasks :
1. Simply find the "2" secret codes that would pass ALL the tests.
2. Reverse the complete algorithm for checking the code.
3. Write a descent tutorial.

IMPORTANT :: If you happen to find a numeric secret-code that passes Test#3 but is negative, e.g. -8, that won't be accepted. The solution by DoomsDay mentioned above considers -8 as a valid secret-code. But that's NOT acceptable. After receiving solution from DoomsDay, I checked my source code again and found that negative codes get accepted due to a problem with flushing the input.

IMPORTANT :: Explain in your solution, how you found "the" secret code that would pass Test #3. Tests #1, #2 are easy enough. NO BRUTE-FORCING.

Readers, if you solve this, please upload your solution to CrackMes.de.