var num=0;

imgArray = [
  ['images/1.jpg','information', 'The beautiful mountains'],
  ['images/2.jpg','interference','The crystal clear lake'],
  ['images/3.jpg','interference','The crystal clear lake'],
  ['images/4.jpg','interference','The crystal clear lake'],
  ['images/5.jpg','interference','The crystal clear lake'],
  ['images/6.jpg','interference','The crystal clear lake'],
  ['images/7.jpg','interference','The crystal clear lake'],
  ['images/8.jpg','interference','The crystal clear lake'],
  ['images/9.jpg','interference','The crystal clear lake'],
  ['images/10.jpg','interference','The crystal clear lake'],
  ['images/11.jpg','interference','The crystal clear lake'],
  ['images/12.jpg','interference','The crystal clear lake'],
  ['images/13.jpg','interference','The crystal clear lake'],
  ['images/14.jpg','interference','The crystal clear lake'],
  ['images/15.jpg','interference','The crystal clear lake'],
  ['images/16A.jpg','interference','The crystal clear lake'],
  ['images/16B.jpg','interference','The crystal clear lake'],
  ['images/17.jpg','interference','The crystal clear lake'],
  ['images/18.jpg','interference','The crystal clear lake'],
  ['images/19.jpg','interference','The crystal clear lake'],
  ['images/20.jpg','interference','The crystal clear lake'],
  ['images/21.jpg','interference','The crystal clear lake'],
  ['images/22.jpg','interference','The crystal clear lake'],
  ['images/23.jpg','interference','The crystal clear lake'],
  ['images/24.jpg','interference','The crystal clear lake'],
  ['images/25.jpg','interference','The crystal clear lake'],
  ['images/26.jpg','interference','The crystal clear lake'],
  ['images/27.jpg','interference','The crystal clear lake'],
  ['images/28.jpg','interference','The crystal clear lake'],
  ['images/29.jpg','interference','The crystal clear lake'],
  ['images/30.jpg','interference','The crystal clear lake'],
  ['images/31.jpg','interference','The crystal clear lake'],
  ['images/32.jpg','interference','The crystal clear lake'],
  ['images/33.jpg','interference','The crystal clear lake'],
  ['images/34.jpg','interference','The crystal clear lake'],
  ['images/35.jpg','interference','The crystal clear lake'],
  ['images/36.jpg','interference','The crystal clear lake'],
  ['images/37.jpg','interference','The crystal clear lake'],
  ['images/38.jpg','message','The lonesome, barren tree']
  
]

function slideshow(slide_num) {
  document.getElementById('mypic').src=imgArray[slide_num][0];
  document.getElementById('mypic').alt=imgArray[slide_num][1];
}

function slideshowUp() {
  num++;
  num = num % imgArray.length;
  slideshow(num);
}

function slideshowBack() {
  num--;
  if (num < 0) {num=imgArray.length-1;}
  num = num % imgArray.length;
  slideshow(num);
}