Eye e[];
 
int num=5;
 
void setup()  
{
  size(500, 500);
  e=new Eye[num]; // need to say how long Eye[] actually is
  for(int i=0;i<num;i++){ // Arrays start from 0, so you want from 0 to num-1 for num entries.
    e[i]=new Eye(i*50,i*50,50);
  }
}
 
void draw()  
{
  background(102);
  for(int i=0;i<num;i++){ // again i=0; i<num
    e[i].update(mouseX,mouseY);
    e[i].display();
  }
}
 
class Eye  
{
  int ex, ey;
  int size;
  float angle = 0.0;
   
  Eye(int x, int y, int s) {
    ex = x;
    ey = y;
    size = s;
  }
  
  void update(int mx, int my) {
    angle = atan2(my-ey, mx-ex);
  }
   
  void display() {
    pushMatrix();
    translate(ex, ey);
    fill(255);
    ellipse(0, 0, size, size);
    rotate(angle);
    fill(153);
    ellipse(size/4, 0, size/2, size/2);
    popMatrix();
  }
}