constructor (set the stack length here)
Moves peek pointer to index
Pops an element from stack
Reads n number of elements from stack, in reverse order (i.e: [nth-last pushed, (n-1)th-last pushed, ..., last pushed])
pushes an element to stack
pushes elements to stack. First in array is pushed first
Writes a value to index
number of elements in stack
a simple array based stack
no bound checking is done, so be careful