Re: Airplane Seating Problem
First problem: You have defined choice as a char[2]. The first major issue here is that you expect the user to enter, for instance, "1c", which requires 3 characters to store {'1', 'c', 0}. The second is that the user may enter something else entirely, like "Hello", and if they do they will totally trash your variables. In the worst case, they could use a buffer overflow attack to gain control of your program and make it do anything they want.
If your teacher allows it, I would recommend making choice a std::string as this will fix both problems. You should verify that a valid seat is entered, however. If you can't used strings, then you should explicitly limit the number of characters that can be read. This is easy to do using scanf, but I don't recall the exact mechanism for cin right now.
After you have the input, you need to interpret it. Validate that only 2 characters were entered, that the first one is a digit between '1' and '7', and that the second is a letter either between 'A' and 'D' or between 'a' and 'd'. Finally, you need to convert these characters to indexes.
For the digit, you should subtract the character '1' to get an index between 0 and 6. For the letter, force it to lowercase using tolower, then subtract 'a' to get an index between 0 and 3.