Increment variable up and down and print it.

fred01.ino

//Variables go first
int fred = 0;
int fredDir= 0; //0 means fred is going up. 1 for down

//setup runs once
void setup() {
}

//draw happens over and over
void draw() {
  
  if (fredDir == 0) { //this code only happens if fred is waxing
    fred = fred + 1; //add one to fred
    if (fred == 256 ) { // if fred gets to 256 change fredDir
      fredDir = 1;
    }
  }


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

  println(fred);
}