Can anyone find the error?

I’ve been trying to make a function that draws a spiral based on the following parameter:

void spiral(int N, float radius, flat step);

The problem I’m having is that I want to be able to control the size of the spiral by mean of the radius. At this moment I can’t see why the figure gets bigger as I increment the N.

void spiral(int N, float radius, flat step){

float currRad = step;

float angle = 360.0 / N;

float currAngle = 0.0;

float prevX = currRad, prevY = 0;

float currX = 0, currY = 0;

glBegin(GL_LINES);

for(; currRad < rad; currRad += step){

currAngle += angle;

currX = prevX + currRad*cos( PI*currAngle / 180.0);

currY = prevY + currRad*sin( PI*currAngle / 180.0);

glVertex2f(prevX, prevY);

glVertex2f(currX, currY);

prevX = currX;

prevY = currY;

}

glEnd();

}

Ok what is the part of the math I’m missing here?