infix_prefix_postfix.rb

#Ruby
def to_post_pre_fix(infix, isPost = true)
	op_stack = []		#宣告成stack
	return_str = ""		#宣告成string
	index_i=0
	while (index_i < infix.size)
		if (infix[index_i] == ")")
				return_str << op_stack.pop	#string operator add to back
		elsif ("+-*/".include? infix[index_i])
			isPost ? op_stack.push(infix[index_i]) : return_str << infix[index_i]
		elsif (infix[index_i] == "(")
			#do nothing
		else	
			isPost ? return_str << infix[index_i] : op_stack.push(infix[index_i])
		end
		index_i += 1
	end
	return return_str
end

infix = "((a+(b*d))+(c/d))"
puts infix.inspect
puts "postfix =>" + to_post_pre_fix(infix)
puts "prefix  =>" + to_post_pre_fix(infix, false)