Question

What is the appropriate function that shows how many are there in an array?

int a[10];
a[0] = 1;
a[1] = 3;

So I want something that shows size of a = 2.

Answer 1

Sounds like you need a dynamically resizable array:

std::vector<int> a;

a.push_back(1);
a.push_back(3);

std::cout << a.size(); // 2