Data Types and Sqrt()

[ebitdamonster]

Hey guys,

I'm working on plotting a circle using two stepper motors. One controls the X axis, the other controls the Y axis. Pretty simple setup.

Here's the section of my code that is intended to draw one quadrant of the circle:

void circle(long r){
  Serial.println("Starting the circle.");
  long r2 = sq(r);
  Serial.println("Radius squared: ");
  Serial.println(r2);
  for (int i=0;i<r;i++){
    x.step(1);
    curx+=1;
    long expy = (sqrt(r2 - (sq(curx))))+1;
    y.step(expy-cury);
    cury = expy;
    Serial.println();
    Serial.print("  X: "+String(curx));
    Serial.print("  Y: "+String(cury));
  }
  delay(10000);
}

The problem is that when I graph the outputted points, it's not circular, even though based on my understanding of the code, I feel like it should be.

I threw the datapoints in Excel just to visualize it, peradventure the machine I built was just imprecise. Plotting it in Excel confirmed the issue:

Is there something about the sqrt() function returning a float that could cause this much of an elongation in my circle?

I've been staring at this all afternoon, just need a different pair of eyes. TIA!