array method

* create
    * create: 
* add (N/A)
* change
    * swap: swaps all elements of one array with other
    * fill: fill the entire array with a particular value
* query
    * at: get the element by the specified index
    * front: get the first element
    * back: get the last element
    * size: return the number of elements
    * empty: check an array is empty or not
* delete (N/A)
* iterator