# File: calc.py
# Simple calculator
#
# Matt Bishop, ECS 10, Winter 2012
#

############
# 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
    temp = input("Number %d: " % n)
    #
    # 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!")
        temp = input("Number %d: " % n)
    #
    # 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
    what = input("What do you want to do (+ - * / % // ** 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 operatio--try again")
        what = input("What do you want to do (+ - * / % // ** 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)
            operand2 = getnum(2)
            # 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()