I'm still getting to grips with Ruby, but I think I'm doing well. My
last post generated a lot of positive comments/advice which really
helped me, so I thought I'd post some more of my code to try and repeat
that!
The following is a method which will convert an infix expression (1+1)
to a postfix expression (1 1 +). It expects a string and returns an
array. Once again I'd really appreciate your comments.
def postfix(expression)
precedence = {nil=>0,40=>0,42 =>2, 43=>1, 45=>1,47=>2}
output = Array.new
stack = Array.new
temp = ''
expression.each_byte do |asc|
case asc
when 41
output.push(temp)
temp = ''
loop{
if stack.empty? == false
popped = stack.pop
if popped == 40
break
else
output.push(popped.chr)
end
else
raise 'Missing "("!'
end
}
when 40,42, 43, 45, 47 #*+-/
output.push(temp)
temp = ''
unless asc == 40
p_asc = precedence[asc]
loop{
if (p_asc > precedence[stack.last])
break
else
output.push(stack.pop.chr)
end
}
end
stack.push(asc)
else
temp += asc.chr
end
end
stack.each{|asc| output.push(asc.chr)}
!output.include?('(') or raise 'Missing ")"!'
output.delete('')
output
end
···
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