Asking Small Advice for our c++ program security

Should I hide license key (stored in string format) in my EXE file as Chr Numeric?

waiting for answers please.
Just an exampe:

Our Software (Exe program) - which has paid version.
After installing the it, the program asks for an activation code for a "Question".
For example "what is the Answer for :0503"
The server and The program also contains a Big Long Serial key like:
"AABBBUQZDCUOQSCOUQZWBCOHCBOQIWOIQBCOQUIZWGOUIE ... "

When User buys our program, he enters the number showed above (0503) on our website,
and the server will tell the answer after paying.
The First two digits (05) means>: Goto the 05th Character in the big serial code, and the answer is next (03) letters.
After paying it theprogram shows to user. "UQZ"
User pastes it to the Program and it works.
The Whole Big serial key is Visible in our Exe if you open with a notepad,
however users don't know how the system works.

Would it be safe For example instead of "AABB..."
So instead of Serialkey$ = "AABB..." using
n = Int(RAND*100)+1
Serialkey[1]=65 * n // 65 is the ASCII code of Letter A
Serialkey[2]=65 * n // 65 is the ASCII code of Letter A
Serialkey[3]=66 * n // 66 is the ASCII code of Letter B
Serialkey[....

Serialkey$ = CHR$(Serialkey[1] /n) + CHR$(Serialkey[2] /n) + CHR$(Serialkey[3] /n) ...

Thanks for your answer,

more Details after milestone.

Sincerly Yours