Well yes I know that much, but like the requirement says. A dynamic array by the type bool is needed in order to mark the positions of the words that are taken. So in other words if the user inputs 4 and 5, and 4 and 5 are already taken, the bool array is there to let the user know that 4 and 5 are already taken and does not exist anymore. Atleast that's how I understand it.
All you need to do is create a new array, call it "placeTaken" which is a bool or int array the same size as game. Then when a and b are selected as in my program just make placeTaken[a] = true or 1 whatever assuming you initialise placeTaken with 0's. You can use that array to make the various tests.