Quadrilateral Centroid Algorithm

Oh men... This time google wasn't helping much...

I was looking for an algorithm to find the centroid from a quadrilateral polygon. It wasn't necessary to be a general, any polygon, centroid algorithm... just one which give me the centroid of a regular convex quadrilateral. It was hard to find something that simple. But finally, here is.
The following code is a C example on how to compute the area and the centroid from a regular convex quadrilateral polygon:

#include<stdio.h>

int main(void){
  float verticesX[5];
  float verticesY[5];
  float centroidX = 0;
  float centroidY = 0;

  verticesX[0] = 3.58; verticesY[0] = 1.90;
  verticesX[1] = 4.48; verticesY[1] = 1.88;
  verticesX[2] = 4.56; verticesY[2] = 2.71;
  verticesX[3] = 3.64; verticesY[3] = 2.74;
  verticesX[4] = 3.58; verticesY[4] = 1.90; // Repeat the first vertex


  int i, k;
  float area = 0.0f;
  float tmp = 0.0f;
  
  for (i = 0; i <= 4; i++){
    k = (i + 1) % (4 + 1);
    tmp = verticesX[i] * verticesY[k] - 
          verticesX[k] * verticesY[i];
    area += tmp;
    centroidX += (verticesX[i] + verticesX[k]) * tmp;
    centroidY += (verticesY[i] + verticesY[k]) * tmp;
  }
  area *= 0.5f;
  centroidX *= 1.0f / (6.0f * area);
  centroidY *= 1.0f / (6.0f * area);
  printf("Centroid = (%1.2f, %1.2f),  area = %1.2f\n", centroidX, centroidY, area);

  return 0;
}