What is the best way to define a class?

Question

C++ / C#

what is the best way to declare a class, globally or inside the right blocks?
banal example written now:

class test_t 
{
public:
int a;
};
/////
struct structure_t
{
test_t test;
};

//

void preset(int& val)
{
test_t test;
...
}

Answer 1

If the class describes a large resource-intensive object, then it is possible globally, but it is better to use the singleton pattern.
In other cases - locally.