# File: calc.py
# Simple calculator
#
# Matt Bishop, COSMOS 2012, Cluster 4
#

############
# Supporting functions
#
# Does str contain a floating point number?
#
# PARAMETER: str: contains a string
# RETURNS: True -- the string in str represents a floating point number
#          FLASE -- it does not
# HOW IT WORKS: it tries to convert the string to a float
# If there's a ValueError exception, it's not a float
# If there isn't, it is
#
def isstrfloat(str):
	try:
		# do the conversion if you can
		value = float(str)
	except ValueError:
		return False
	else:
		return True

#
# Return a float that the user inputs
#
# PARAMETER: n: integer printed as part of the user prompt
# RETURNS: floating point number that the user entered
# HOW IT WORKS: read a string; if it's not a float, try again
#
def getnum(n):
	# prompt for, and read, a string
	try:
		temp = input("Number %d: " % n)
	except EOFError:
		return "q"
	#
	# see if it's a floating point number
	while not isstrfloat(temp):
		# nope -- get another string from the user
		print("You need to enter a number!")
		try:
			temp = input("Number %d: " % n)
		except EOFError:
			return "q"
	#
	# it corresponds to a float -- return the corresponding float
	return float(temp)

#
# Return a Python arithmetic operator (or 'q' for quit) that the
# user inputs
#
# PARAMETER: none
# RETURNS: a string containing a string representation of a Python
#          arithmetic operator
# HOW IT WORKS: read a string; if it's not an operator, try again
#
def getop():
	# prompt for, and read, a string
	try:
		what = input("What do you want to do (+ - * / % // ** q)? ")
	except EOFError:
		return "q"
	#
	# see if it's a Python operator or 'q' for quit
	while what != '+' and what != '-' and what != '*' and what != '/' and \
			  what != '//' and what != '%' and what != '**' and what != 'q':
		# nope -- get another string from the user
		print(what, "is not a valid operation -- try again")
		try:
		    what = input("What do you want to do (+ - * / % // ** q)? ")
		except EOFError:
		    return "q"
	#
	# it corresponds to an operator or 'q' -- return it
	return what

#
# The main function -- do the calculations until told to quit
#
def main():
	#
	# announce the program
	print("Welcome to the calculator! ")
	#
	# loop until user says to quit
	cmd = 'start'
	while cmd != "q":
		# get the user's desired operation
		cmd = getop();
		# if it's to quit, skip to the end of the loop
		if cmd != 'q':
			#
			# we are to do a computation
			# get the two operands
			operand1 = getnum(1)
			if operand1 == "q":
							return
			operand2 = getnum(2)
			if operand2 == "q":
				return
			# now do the operation and show the result
			if cmd == '+':          # add
				print(operand1, "+", operand2, "=", operand1 + operand2)
			elif cmd == '-':        # subtract
				print(operand1, "-", operand2, "=", operand1 - operand2)
			elif cmd == '*':        # multiply
				print(operand1, "*", operand2, "=", operand1 * operand2)
			elif cmd == '/':        # divide, remainder as a fraction
				print(operand1, "/", operand2, "=", operand1 / operand2)
			elif cmd == '%':        # take the remainder
				print(operand1, "%", operand2, "=", operand1 % operand2)
			elif cmd == '//':       # divide, discard the remainder
				print(operand1, "//", operand2, "=", operand1 // operand2)
			elif cmd == '**':       # raise to a power
				print(operand1, "**", operand2, "=", operand1 ** operand2)
			else:
				# SHOULD NEVER HAPPEN -- anything other than the operators
				# and 'q' should be discarded by the getop() routine -- but
				# if that's changed and this function is not updated . . .
				print("Unknown operation", cmd)


main()