In the C++ programming language write a program capable of playing Tic-Tac-Toe against the user. Your program should use OOP concepts in its design. You can use ASCII art to generate and display the 3x3 playing board. The program should randomly decide who goes first computer or user. Your program should know and inform the user if an illegal move was made (cell already occupied). The program should also announce if one of the players wins or if a draw is achieved.