Meaning of default init and value init?

Question

I am very confused by c++ ways of initializing variables. What is the difference if any, between these:

int i; // does this make i uninitialized?
int i{}; // does this make i = 0?
std::array<int, 3> a; // is a all zeros or all uninitialized?
std::array<int, 3> a{}; // same as above?

Thanks for clarifying

Answer 1

int i; // does this make i uninitialized?

Yes, if in local scope and not in global scope.

int i{}; // does this make i = 0?

Yes, always.

std::array<int, 3> a; // is a all zeros or all uninitialized?

Uninitialized if in a local scope, but zeroed of in global scope, i.e., same as your first question.

std::array<int, 3> a{}; // same as above?

All values are default initizlized, i.e., all three elements are zeroed.