validating an array

[saint1947]

I have written a simple switch menu that parses data stored in an array of structure objects. The first option allows the user to enter data and following options manipulate the data. What sort of validation can I do to ensure that option 1 has been used (entering valid data into the array) before other options on the menu can be chosen. I'm thinking it should be a simple boolean expression (maybe an if statement) within the case statements for the menu options. But I don't know what I can check to determine whether or not the array contains valid data.