Pitch, Yaw, and Roll

Multiple times in the past, I've tried to make a 3D engine for the heck of it because my 3D skills are nonexistent, and with every engine I make, my knowledge increases. Well, I've come quite far with this one but I'm puzzled on how to fix this bug I've been having with rotation.

		'pitch
		If x<>0
			If v.z=0
				If v.y>0 angle=90 Else angle=270
			EndIf
			If v.z<>0 angle=ATan(v.y/v.z)+x
			dist=Distance2D(v.z,v.y,0,0)
			v.z=Cos(angle)*dist
			v.y=Sin(angle)*dist
		End If

This is part of my function TurnCamera, and is the portion which handles pitch. X is the angle it needs to turn, and v.x, v.y, and v.z are the coordinates of each vertex.
I'm having two problems. First, when using ATan(v.y/v.z), v.z is often zero, leaving me with NaN. That is why it does a check for if v.z is zero and determines the angle based on y if so. But the algorithm doesn't work anyway. What is wrong with my equation?

I don't know for the "algorithm", but you should use Atan2 instead of Atan. This will remove the division by zero problem.

Thanks much for your help, hopefully that solves the problem.

Alright, rotation works quite nicely now, but I've run into another problem.
My scaling function is not working as I intended for it to -

	Method Scale(x#,y#,z#)
			'find center (average xyz of the vertecies)
			Local avgx#=0,avgy#=0,avgz#=0,scal%
			For scal%=1 To vertex_count
				avgx:+ver[scal].x-CamX
				avgy:+ver[scal].y-CamY
				avgz:+ver[scal].z-CamZ
			Next
			avgx:/Float(vertex_count)
			avgy:/Float(vertex_count)
			avgz:/Float(vertex_count)
			Print avgx+","+avgy+","+avgz
			'scale it
			For scal%=1 To vertex_count
				ver[scal].x= (((ver[scal].x-avgx)*x)+avgx) +CamX
				ver[scal].y= (((ver[scal].x-avgy)*y)+avgy) +CamY
				ver[scal].z= (((ver[scal].x-avgz)*z)+avgz) +CamZ
			Next
	End Method