for (var i in arr) {console.log("Hello, "+arr[i]+"!")} //for 


var i=0;
while (i<arr.length){console.log("Hello, "+arr[i]+"!"); i++;} //while 正序


var i=arr.length-1
while (i>=0){console.log("Hello, "+arr[i]+"!"); i--;} //while 倒序