for (var key in arr.reverse()) {
  console.log(`hello, ${arr[key]}!`);
}
for (var key in arr) {
  console.log(`hello, ${arr[key]}!`);
}
var n = 0;
while (n < arr.length){
  console.log(`hello, ${arr[n]}!`);
  n++;
}
var n = 0;
while (n < arr.length){
  console.log(`hello, ${arr.reverse()[n]}!`);
  n++;
}