This program implements a simple key for identifying an unknown sample of plastic which you may have. It does this by asking a series of questions, each of which has a yes/no answer. The program is adapted so that the user can type Y, N, yes, no YES, NO etc. and the program will still understand. The structure of the key which the program implements is shown below, but in order to avoid having to embed various if statements inside one another, each question is given a number, and if statements corresponding to the different questions are only triggered if their number comes up. Look at the source code to see what I mean.