I have a 2D vector as defined by the classes below. Note that I've used classes because I'm trying to program a genetic algorithm such that many, many 2D vectors will be created and they will all be different. class Quad: public std::vector<int> { public: Quad() : std::vector<int>(4,0) {} }; class QuadVec : public std::vector<Quad> { }; An important part of my algorithm, however, is that I need to be able to "mutate" (randomly change) particular values in a certain number of randomly chosen 2D vectors. This has me stumped. I can easily write code to randomly select the value within the 2D vector that will be selected for "mutation" but how do I actually enact that change using classes? I understand how this would be done with one 2D vector that has already been initialized but how do I do this if it hasn't? Please let me know if I haven't provided enough info or am not clear as I tend to do that. Thanks for your time and help!