C++ Variable question

Question

What does it mean when there are curly braces right after a variable name?
Like this:
int a{12}

I've also seen something like this:
int a{{12}}

What are these?

Answer 1

There is no difference in this case, they all initialize a with 12.
It's just what you prefer.

However you should be aware that they cannot be interchanged everywhere.

For example
std::vector<int> v(10); // Creates a vector with 10 elements
std::vector<int> v{10}; // Creates a vector with 1 element

int a{}; // a = 0
int a(); // a is a function declaration

So yea, learn about the pitfalls of each of them.
Personally I prefer the =.

Answer 2

https://www.geeksforgeeks.org/uniform-initialization-in-c/

Also the second example is illegal in this case.
std::array<int,10> a{{12}}; is allowed here though.

Answer 3

Exclude the last one. Brain was on auto pilot. Lol

Answer 4

interesting
So what's the difference between:
int a=12
int a(12)
int a{12}?