#----------------------------------------------------------------------
# February 11, 2019
#----------------------------------------------------------------------

#**********************************************************************
# Task #1: Write a function that asks the user to enter a number
# that is positive or zero, and if not continuously asks until
# they do.  Return the correctly entered number.
#**********************************************************************

#----------------------------------------------------------------------
# Solution #0: Function kind of works, as long as the user behaves
# and enters a positive number on either the first or second try.
#
# How to Call: X = GetAPositiveNumber0() 
#
# Problem: Function only asks ***once*** if the number is negative,
# so the user could enter a negative number the second time that is
# returned.  FAIL.  Function does NOT work as intended.
#----------------------------------------------------------------------

def GetAPositiveNumber0 ():
    N = float(input("Please enter a non-negative number --- "))
    if N < 0.0:
        N = float(input("Please enter a non-negative number --- "))
    return N

#----------------------------------------------------------------------
# Solution #1: Function does everything correctly by using a while
# to continuously ask for a new number as long as it is entered as
# a negative.
#
# How to Call: X = GetAPositiveNumber1() 
#
# Problem: The message text is typed in twice.  If it needs to be
# changed, it has to be changed identically in two different places.
#----------------------------------------------------------------------

def GetAPositiveNumber1 ():
    N = float(input("Please enter a non-negative number --- "))
    while N < 0.0:
        N = float(input("Please enter a non-negative number --- "))
    return N

#----------------------------------------------------------------------
# Solution #2: The text message is saved as a local variable and that
# variable is used where needed.  If the message must be changed,
# there is only one place that needs editing.
#
# How to Call: X = GetAPositiveNumber2() 
#
# Problem: The N = float(input(Message)) statement still appears twice.
#----------------------------------------------------------------------

def GetAPositiveNumber2 ():
    Message = "Please enter a non-negative number --- "
    N = float(input(Message))
    while N < 0.0:
        N = float(input(Message))
    return N

#----------------------------------------------------------------------
# Solution #3: By establishing N as an illegal value first, the code
# forces the while-loop to go at least once, getting a new value for N.
#
# How to Call: X = GetAPositiveNumber3() 
#
# Problem: Changing the message means changing the code.  (This has
# been a problem all along; we are just now getting to addressing it.)
#----------------------------------------------------------------------

def GetAPositiveNumber3 ():
    Message = "Please enter a non-negative number --- "
    N = -1
    while N < 0.0:
        N = float(input(Message))
    return N

#----------------------------------------------------------------------
# Solution #4: Now the Message variable is not established inside the
# function, but its value is passed in from outside.  The call to
# the function now *must* give it a string as an actual parameter.
#
# How to Call: X = GetAPositiveNumber4("Please enter a value --- ") 
#              X = GetAPositiveNumber4("I want a positive --- ")
#              X = GetAPositiveNumber4("You are a kumquat --- ")
#
# Problem: You have to always give the parameter a value, even if it
# is the same as all other calls throughout your program.
#----------------------------------------------------------------------

def GetAPositiveNumber4 (Message):
    N = -1
    while N < 0.0:
        N = float(input(Message))
    return N

#----------------------------------------------------------------------
# Solution #5: The value of Message can still be passed in as a custom
# string, but it can be omitted and if so the default value will be
# used.
#
# How to Call: X = GetAPositiveNumber5("Please enter a value --- ") 
#              X = GetAPositiveNumber5("I want a positive --- ")
#              X = GetAPositiveNumber5("You are a kumquat --- ")
#              X = GetAPositiveNumber5()    # uses the default string
#
#----------------------------------------------------------------------

def GetAPositiveNumber5 (Message="Enter a positive number --- "):
    N = -1
    while N < 0.0:
        N = float(input(Message))
    return N






#**********************************************************************
# Task #2: Write a function that accepts a student score as a parameter
# and prints the corresponding grade (print an "A" for scores >= 90,
# print a "B" for scores >= 80, etc.)
#**********************************************************************

def PrintGrade (Grade):
    if Grade >= 90:
        print ("A")
    else:
        if Grade >= 80:
            print ("B")
        else:
            if Grade >= 70:
                print ("C")
            else:
                if Grade >= 60:
                    print ("D")
                else:
                    print ("F")
    return

#----------------------------------------------------------------------
# Notice the indentation, and that in each case the else is lined up
# with its matching if.
#
# Notice that the function returns without specifying a return value.
# Since this function prints its results on the console, there is
# nothing to return to the code that called it.  In contrast, in all
# of the GetAPositiveNumber variants, the final correct value entered
# by the user was explicitly returned.
#
# This illustrates two types of functions: (1) those that compute
# something and returns a value, and (2) those that do some action
# but have nothing to return.
#
# Final observation: The if-else-if-else... network in PrintGrade
# is fairly large and cumbersome.  Think about what it would look
# like if it had to deal with UMass A-, B+, B-, C+, C-, and D+ grades!
# IS THERE A WAY TO MAKE THIS BETTER?  (See next lecture...)
#----------------------------------------------------------------------