"Missing type specifier - int assumed" cannot be solved by adding "return 0" to the main function

I am trying to figure out how the C++ key word "this" works. I followed the codes below, but it does not pass and show the error of

#include <iostream>
#include <string>

void PrintEntity(const Entity& e);

class Entity
{
public:
    int x, y;

    Entity(int x, int y)
    {
        this->x = x;
        this->y = y;

        PrintEntity(*this);
    }
};

void PrintEntity(const Entity& e)
{
    std::cout << "Entity" << std::endl;
}

int main()
{
    return 0;
}

I reviewed other similar questions, the solutions include adding "return 0" to the Main function or circular dependency. But I don't think these solutions apply for me. Please help me solve it, thanks!