I really suggest you spend your time learning how to use Triangle. It's just that much more clean than approximating stuff with zig-zagging them in an SSC.
That being said, here's a few pointers to get you going with your pentagon:
First you have to ask, How can a <enter your shape here> be created with triangles? In the case of a pentagon that's pretty easy once you draw a pentagon on paper:
Blue numbers identify triangles and red numbers identify vertices (corners).
So you are going to have 3 triangles.
So in your Init box goes
n = 3;
You also need the coordinates for those triangles, preferably in x, y and z. So I would suggest to use megabuf() since that can be indexed and you can access it more easily later with the help of counters (more about them later).
So write down the coordinates for your pentagon-triangles (or calculate them live - which I will do below) and write the values to a megabuffer array, like so:
crcl5th = 2*$PI/5; // precalculate the step size around a circle
size = 1;
point1x = sin(crcl5th*0)*size; point1y = cos(crcl5th*0)*size;
point2x = sin(crcl5th*1)*size; point2y = cos(crcl5th*1)*size;
point3x = sin(crcl5th*2)*size; point3y = cos(crcl5th*2)*size;
point4x = sin(crcl5th*3)*size; point4y = cos(crcl5th*3)*size;
point5x = sin(crcl5th*4)*size; point5y = cos(crcl5th*4)*size;
// x coordinate ------------- y coordinate ------------- z coordinate
// triangle 1
// triangle 2
// triangle 3
All this goes into your init section as well, except if you want to modify the coordinates (for example if your pentagon should rotate, or move in any other way.
Now comes the tricky part. You need to access these 3 triangles in your point/triangle code
Every time the triangle section gets evaluated it expects you to give it 3 points in 2D, that is:
x1 = someval; y1 = someval;
x2 = someval; y2 = someval;
x3 = someval; y3 = someval;
Additionally you can specify the triangles color with:
red1 = redval;
blue1 = blueval;
green1 = greenval;
(There is no red2/blue2/green2 and red3/blue3/green3, don't bother...)
Now how do you access the coordinates from the megabuf()?
Well you use a counter. That counter should count in steps of 9, because each time in the triangle section, you want to use 9 different values (we have Z-coordinates, but we throw them away for now, when you add 3D-rotation you will need them again). So, in the frame section set your counter to zero:
counter = 0;
so that every frame the counter will be reset and the pentagon drawn correctly.
Now in the triangle section you read your values from the megabuffer into the coordinates, increase the counter and you're done:
x1 = megabuf(counter); y1 = megabuf(counter+1); // you can add z1/2/3 here if needed
x2 = megabuf(counter+3); y2 = megabuf(counter+4);
x3 = megabuf(counter+6); y3 = megabuf(counter+7);
counter = counter+9;
Voila, if everything went well it should show you a white pentagon now.
I have to admit, I haven't tested this, but I've done it so many times I'm pretty sure it works. If you think something is off, tell me, but check first if you followed the steps correctly.