This is the readme file for Calculator Project

	i.The Calculator file contains 3 three files which implements a simple calculator.
	ii.Using linked-list implemented Stack data structure to utilize the calculator.
	
	iii.3 scripts:
  		a)lliststack.py: linked-list implementation of Stack ADT
		b)extopostfix.py: receive an input infix expression and change it into a postfix expression.
		c)postfix.py: receive a postfix expression and calculate the result, then return it back.(the postfix expression is always
comes from the result of the extopostfix.py)
	
	iv.how to use the calculator?
		run "python postfix.py" then input a infix expression then press enter.