var photo=new Array()
var num=0
photo[0]="images/rock01.jpg"
photo[1]="images/rock02.jpg"
photo[2]="images/rock03.jpg"
photo[3]="images/rock04.jpg"
photo[4]="images/rock05.jpg"
photo[5]="images/rock06.jpg"
photo[6]="images/rock07.jpg"
photo[7]="images/rock08.jpg"
photo[8]="images/rock09.jpg"
photo[9]="images/rock10.jpg"
photo[10]="images/rock11.jpg"
photo[11]="images/rock12.jpg"
photo[12]="images/rock13.jpg"
photo[13]="images/rock14.jpg"
photo[14]="images/rock15.jpg"
numero=num+1

function precedente() {
  if (num>0) {
    num--
      document.image.src=photo[num];
    numero=num+1
  }
}
function suivante() {
  if(num<photo.length-1) {
    num++
      document.image.src=photo[num];
    numero=num+1
  }
}