It means you've done something in your code very wrong. std::out_of_range generally means you've tried to access part of a vector or some other such container that doesn't exist. For example, trying to access element 20 of a vector that only has 10 elements in it.
the code is very long so I don't wanna make anyone bother to go all over it . Its my last option and before that can I make a function to return a vector??because the code is about bulding a class which has sequential functions that use the vector created by the first function FormVector.
but FormVector returns void. I assumed that it just prepares the vector so the other functions can use it