/*
LOOPS: WHILE, FOR, FOR-IN
While loops are less popular than for loops.
They are more manual and work better with numbers.
*/

var count = 0;
while (count < 11) {
    count++; // if you will miss this part, program will crash
} // prints 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. It stopped at 11.

//For loop is good for looping forward over Array:

var arr = [1, 2, 3, 4, 5];
for(var i = 0; i < arr.length; i++) {/* start the loop when index is at 0;
go as long as the index is smaller than the length of an Array (that means no more than 6 indeces);
increment the index by 1*/
    print('index:' + i); // prints: at index: 0 is 1, at index: 1 is 2 etc.
    var element = arr[i];
}

function print(value) {
    console.log(value);
}
//To loop backwards over Array, you need to reverse the condition:

for(var j = arr.length - 1; j > -1;j--) { /* start the loop when index (j) equals to the last
Array's element; continue until index (j) is bigger than -1; decrement the index (j) by 1 */
    print('index:' + j) ; // at index: 4 is 5, at index: 3 is 4 etc
    var element = arr[j];
}

//For-in is designed for looping over Object

var object = {
    one: 'a', //key and value pairs
    two: 'b',
    three: 'c'
};

for(var key in object){
    print('key:' + key); // dynamically accessing the value
    print('value ' + object[key]);// must use array for dynamic looping
}

print(object['two']); // prints 'b'
object.four = 'd'; // we are adding more keys in to the Object, using dot notation
object['five'] = 'e'; // we could add more keys with such syntax, too

var keys = (Object.keys(object).length);
print(keys); // prints 5 (keys), because we added extra two at the end
}