Here are some cheats and tips for the game Operation C.
Level select:
Press Up(2), Down(2), Left, Right,
Left, Right, B, A, B, A,
Start at the title screen.
Ten lives:
Press Up(4), Down(4), Left(4), Start
at the title screen.
Sound test:
Press Up, Down, Left, Right, A,
B, Start at the title screen.