# File:    recurPractice.py
# Author:  Dr. Gibson
# Date:    4/19/2017
# Section: N/A
# E-mail:  k.gibson@umbc.edu
# Description:
#   This file contains python code that recursively implements
#   a "valid grade getter" and has multiple implementations of
#   a recursive "list summer" function

# recGetGrade() prompts the user for a grade between 0 and 100
# Input:        none; (0 and 100 are default, not passed in)
# Output:       grade; an integer between 0 and 100, inclusive
def recGetGrade():
    grade = int(input("What is your grade? "))

    # BASE CASE: valid grade
    if grade >= 0 and grade <= 100:
        return grade

    # RECURSIVE CASE: invalid grade
    else:
        print("That's not valid; must be between 0 and 100, inclusive.")
        # RECURSIVE CALL (with return, since a value is being returned)
        return recGetGrade()


# recSumList1() sums a list by adding the first element to the rest
#               of the list recursively
# Input:        currList; a list of integers
# Output:       total of the list's contents
def recSumList1(currList):

    # BASE CASE: list is empty, nothing more to sum together
    if len(currList) == 0:
        return 0

    # RECURSIVE CASE: list is not empty, keep going
    else:
        # helps trace what's going on, but not necessary
        print("Adding", currList[0], "to", currList[1:] )

        # RECURSIVE CALL: add first element to sum of rest of list
        return currList[0] + recSumList1( currList[ 1: ] )


# recSumList2() sums a list by keeping track of what index
#               we're at when adding the entire list together
# Input:        theList; a list of integers
#               currIndex; index of contents to be added in next
# Output:       total of the list's contents
def recSumList2(theList, currIndex):

    # BASE CASE: reached the end of the list, stop adding
    if currIndex == len(theList):
        return 0

    # RECURSIVE CASE: not at the end of the list, keep going
    else:
        # helps trace what's going on, but not necessary
        print("Now adding", theList[currIndex], "at index", currIndex)
        # RECURSIVE CALL: add current element, call on next one
        return theList[currIndex] + recSumList2(theList, currIndex + 1)
        



def main():

    myList = [3, 5, 8, 7, 2, 6, 1]

    print("\tAdding the list", myList, "together:")
    ans1 = recSumList1(myList)
    print("The sum of the list is", ans1)


    print("\n\tAdding a different way: ")
    # requires that we give starting index, so start at position 0
    ans2 = recSumList2(myList, 0)
    print("The sum of the list is", ans2)


    print("\n\n\tAsking for a valid grade using recursion:")
    ans = recGetGrade()
    print("You got a grade of", ans)


main()