# Midterm EECS 12 Summer Session I 2006
# Solution
# Mark E. Phair mphair uci.edu
import math # for pow
import string # for letters

####################################################
####### FUNCTIONS ##################################
####################################################

# requirement: function resolve
def resolve(argument):
   """Returns the number if argument is number, does a variable
      lookup if argument starts with a letter"""
   if argument[0] in string.letters: 
      # the first character of argument is a letter, so
      # arugment is a variable name
      if variables.has_key(argument):
         return variables[argument]
      else:
         print 'Unknown variable:', argument
         # requirement: unknown variable returns 0.0
         return 0.0 
   else:
      # the first character of argument is not a letter,
      # therefore it should be a number
      return float(argument)
      

####################################################
############ MAIN ##################################
####################################################
variables = {}
doLoop = True
last = 0 # keep last calculated value
while doLoop:
   # split raw_input immediately, we don't need the full string
   response = raw_input('? ').split(' ') 

   # This whole thing can be probably better be done
   # with a dictionary of function objects, but those
   # had not been taught yet.
   if response[0] == 'exit':
      # we're done!
      doLoop = False

   # standard operations... resolve and perform the op
   elif response[0] == '+':
      last = resolve(response[1]) + resolve(response[2])
      print last
   elif response[0] == '-':
      last = resolve(response[1]) - resolve(response[2])
      print last
   elif response[0] == '*':
      last = resolve(response[1]) * resolve(response[2])
      print last
   elif response[0] == '/':
      last = resolve(response[1]) / resolve(response[2])
      print last
   elif response[0] == 'pow':
      last = math.pow(resolve(response[1]), resolve(response[2]))
      print last

   # storing the last calculated value in a variable
   elif response[0] == 'store':
      variables[response[1]] = last
      print response[1], '=', last

   # clearing out all calculated values
   elif response[0] == 'clear':
      # we can use the empty dictionary method here because
      # the scope is correct. If we were doing this inside
      # of a function, we'd have to use some other method.
      variables = {} 
      print 'Variables cleared.'

   # show all of the calculated values, printed pretty
   elif response[0] == 'showall':
      for key, value in variables.items():
         print key, '=', value

   # the user has entered an operation we don't have
   else:
      print 'Unknown operation.'