Scaling

What is the best way to scale coordinate system with the objects on it. I know i can use SDL_SetRenderScale(), but it only scales the rendering thing. But if i have a mouse based selection, and since the object coordinates themselves arent changing, that would mean that i can click on nowhere and object is selected elsewhere. I tryd using rendercopy by changing the destination rect, but then i need to start changing the X and Y coordinates. Is there any good way to scale so, that i dont have to modify the objects themselves but can getaway by changing the coordinate axsis in the window?