Need tic tac toe game logic or demo application ?

Question

• I need a tic tac toe game logic or sample project in WPF C#. 
• I already developed the User vs User part.
• I want clarification in User vs Computer(cpu) where a computer will select the right step in the game automatically. 

I am just making this app to brush up on the skill in WPF.

 

Thanks in advance.