Drawing Normals as Lines

Hi, I’ve been having real trouble figuring out how to draw normals as lines. Right now for my project I’m working on smoothing out a cylinder. I’ve created normals for the faces and so far it looks fine. I just can’t grasp how to draw lines to indicate where the normals are.
Here’s a snipped of code.
// draw bottom boundary:
p1[0] = ctx; p1[1] = cty; p1[2] = ctz;
p2[0] = ntx; p2[1] = nty; p2[2] = ntz;
p3[0] = 0; p3[1] = -len; p3[2] = 0;
getNormals( p1, p2, p3, topTriangle);
glVertex3d ( cbx, cby, cbz ); glVertex3d ( nbx, nby, nbz ); glVertex3d ( 0, -len, 0 );

This is for the bottom circle of my cylinder.

Any help would be greatly appreciated.

The starting point of the line will be the vertex.
The end point will be thevertex+normal * some_length_factor

This is not a end point. This is just a vector.
p2[0] = ntx; p2[1] = nty; p2[2] = ntz;