To draw this "Vienna sausage" arrangement:

 

You just need the coordinates of the centers and the radius. If you use 1 for
the radius and coordinate axes, you get this:

 

As you see, the centers form a regular hexagon, which is made up of 6
equilateral triangles, and each equilateral triangle is made up of 2
30°-60°-90° right triangles.  So there are 12 30°-60°-90° right triangles.

I used the radius of the circles as 1, but you can make it anything you like.

The shortest side of a 30°-60°-90° triangle is 1 times the length of the radius.
The medium side is sqrt(3) times the length of the radius,
The longest side (the hypotenuse) is 2 times the length of the radius.

That's all you need to write up the C++ coding.

Edwin