Prefix to postfix conversion using stack in ruby

Ruby program for Prefix to postfix conversion using stack. Here problem description and other solutions.

#  Ruby program for
#  Prefix to postfix conversion

#  Stack Node
class StackNode 
	# Define the accessor and reader of class StackNode
	attr_reader :data, :next
	attr_accessor :data, :next
	def initialize(data, top) 
		self.data = data
		self.next = top
	end

end

class MyStack 
	# Define the accessor and reader of class MyStack
	attr_reader :top, :count
	attr_accessor :top, :count
	def initialize() 
		self.top = nil
		self.count = 0
	end

	#  Returns the number of element in stack
	def size() 
		return self.count
	end

	def isEmpty() 
		if (self.size() > 0) 
			return false
		else
 
			return true
		end

	end

	#  Add a new element in stack
	def push(data) 
		#  Make a new stack node
		#  And set as top
		self.top = StackNode.new(data, self.top)
		#  Increase node value
		self.count += 1
	end

	#  Add a top element in stack
	def pop() 
		temp = ""
		if (self.isEmpty() == false) 
			#  Get remove top value
			temp = self.top.data
			self.top = self.top.next
			#  Reduce size
			self.count -= 1
		end

		return temp
	end

	#  Used to get top element of stack
	def peek() 
		if (!self.isEmpty()) 
			return self.top.data
		else
 
			return ""
		end

	end

end

class Conversion 
	#  Check operator
	def isOperator(text) 
		if (text == '+' || text == '-' || 
            text == '*' || text == '/' || 
            text == '^' || text == '%') 
			return true
		end

		return false
	end

	#  Check operands
	def isOperands(text) 
		if ((text >= '0' && text <= '9') || 
            (text >= 'a' && text <= 'z') || 
            (text >= 'A' && text <= 'Z')) 
			return true
		end

		return false
	end

	#  Converting the given prefix expression to 
	#  postfix expression
	def prefixToPostfix(prefix) 
		#  Get the size
		size = prefix.length
		#  Create stack object
		s = MyStack.new()
		#  Some useful variables which is using 
		#  of to storing current result
		auxiliary = ""
		op1 = ""
		op2 = ""
		isValid = true
		i = size - 1
		while (i >= 0) 
			#  Check whether given prefix location
			#  at [i] is an operator or not
			if (self.isOperator(prefix[i])) 
				#  When operator exist
				#  Check that two operands exist or not
				if (s.size() > 1) 
					op1 = s.pop()
					op2 = s.pop()
					auxiliary = op1 + op2 + prefix[i]
					s.push(auxiliary)
				else
 
					isValid = false
				end

			elsif(self.isOperands(prefix[i])) 
				#  When get valid operands
				s.push(prefix[i])
			else
 
				#  Invalid operands or operator
				isValid = false
			end

			i -= 1
		end

		if (isValid == false) 
			#  When have something wrong
			print("Invalid Prefix : ", prefix, "\n")
		else
 
			#  Display calculated result
			print(" Prefix : ", prefix, "\n")
			print(" Postfix  : ", s.pop(), "\n")
		end

	end

end

def main() 
	task = Conversion.new()
	prefix = "+*ab^cd"
	task.prefixToPostfix(prefix)
	prefix = "-+*^%adcex*y^ab"
	task.prefixToPostfix(prefix)
end

main()

Output

 Prefix : +*ab^cd
 Postfix  : ab*cd^+
 Prefix : -+*^%adcex*y^ab
 Postfix  : ad%c^e*x+yab^*-