var photo=new Array()
var num=0
photo[0]="ct1.jpg"
photo[1]="ct2.jpg"
photo[2]="ct3.jpg"
photo[3]="ct4.jpg"
photo[4]="ct5.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
  }
}