Visual C++ :: How To Make A Shape Outside Of Main Function

I know how to define a shape (here, a rectangle) and attach it to a window in C++ as follows:

Code:
#include <Simple_window.h>
void cir() { Circle c(Point(100,100),50); }
int main() {
Simple_window win(Point(100,100),600,400, "test");

[Code] ....

But how to define a shape (say a circle by that cir() function which is) outside of the main() function that is how to create a circle inside of the cir() function and it returns that circle when I called it in my main() function so that I can attach it on the window win to be visible?