Here a character moves back and forth.

arlo01.ino

//Variables go first
int arloX = 200;
int arloY = 350; 
int fredDir = 0;
int look = 0; // extra credit

//setup runs once
void setup() {
  size(400, 400);
}

//draw happens over and over
void draw() {
  background(200);

  //draw Arlo
  fill(255); // fill body with white
  rect(arloX-25, arloY-150, 50, 150); //body
  rect(arloX-100, arloY-190, 200, 40); // arms
  ellipse(arloX, arloY-210, 60, 60); // head
  ellipse(arloX-15, arloY-200, 10, 10); //eyes
  ellipse(arloX+15, arloY-200, 10, 10);
  fill(0); // fill pupils with black
  ellipse(arloX-13-look, arloY-200, 5, 7); //pupils
  ellipse(arloX+17-look, arloY-200, 5, 7);



  if (fredDir == 0) { //this code only happens if fred is waxing
    arloX += 1; //add one to fred
    if (arloX == 300 ) { // if fred gets to 256 change fredDir
      fredDir = 1;
      look = 3;
    }
  }


  if (fredDir == 1) { //this code only happens if fred is waning
    arloX -= 1;
    if (arloX == 100) {
      fredDir = 0;
      look = 0;
    }
  }

  // println(fred);
}