class Car {

  color c;
  float xPos;
  float yPos;
  float xSpeed;

    Car() {
      c = color(155);
      xPos = width/2;
      yPos = height/2;
      xSpeed = 1;
    }

  void display() {
    rectMode(CENTER);
    fill(c);
    rect(xPos, yPos, 20, 10);
  }

  void drive() {
    xPos = xPos + xSpeed;
    if (xPos > width) {
      xPos = 0;
    }
  }
}

Car myCar;

void setup() {
  myCar = new Car();
}

void draw() {
  background(255);
  myCar.drive();
  myCar.display();
}