# while loop

index = 1
while index <= 10:
    print("while loop with controlled condition : " + str(index))
    index += 1           # or index = index + 1


index = 1
while True:
    if index > 10:
        break;
    print("while loop with bad controlled condition : " + str(index))
    index += 1


while input("Do you want to continue (Y/N) ? ") == "Y":
    print("let's continue")


done = ""
while done != "quit":
    print("let's continue -- not done yet")
    done = input("Continue ? (type quit to quit) ")



experts = ["wear", "no", "no", "wear", "wear", "no"]
ctr = 0
while ctr < len(experts):
    expert = experts[ctr]
    if expert == "wear":
        print("shake")
    else:
        print("no")
    ctr += 1


i = 5
while i > 0:
   print(i * i * i)
   i -= 1



# This example illustrates a situation when
# a while loop results in an infinite loop.
# Notice the infinite variable (i.e., counter of the loop)
# and the condition next the a while keyword
#
# Be careful when setting up the condition and whether to increment/decrement the counter
#
# infinite = 1
# while infinite > -1:
#     print(infinite)
#     infinite +=1
#

value = 5
while value >= 0 and value <= 10:
    value = int(input("Enter a number less than 0 or greater than 10 : "))


value2 = -1
while value2 <= -1 or value2 > 10:      # this is the bad case
    value2 = int(input("Give me a number between 0 and 10: "))


list_of_animals = ["dog", "cat", "fish"]
cnt = 0
while len(list_of_animals) > 0:
    print(list_of_animals[cnt])
    list_of_animals.remove(list_of_animals[cnt])       # try comment this line, run, and see what happen


## exercise (while loop)
## consider when does the loop stop
number_of_courses = int(input("Enter the number of courses : " ))
cnt = 1
while cnt <= number_of_courses:
    letter = ""

    grades = input("Enter 3 exams grade : ")
    list_of_grades = grades.split()

    print(list_of_grades)
    print(list_of_grades[0])

    grade_average = (float(list_of_grades[0]) + float(list_of_grades[1]) + float(list_of_grades[2])) / 3

    # determine a letter grade and store it for later use
    if grade_average >= 98:
        letter = "A+"
    elif grade_average >= 93:
        letter = "A"
    elif grade_average >= 90:
        letter = "A-"
    elif grade_average >= 87:
        letter = "B+"
    elif grade_average >= 83:
        letter = "B"
    elif grade_average >= 80:
        letter = "B-"
    elif grade_average >= 77:
        letter = "C+"
    elif grade_average >= 73:
        letter = "C"
    elif grade_average >= 70:
        letter = "C-"
    elif grade_average >= 67:
        letter = "D+"
    elif grade_average >= 63:
        letter = "D"
    elif grade_average >= 60:
        letter = "D-"
    else:
        letter = "F"

    # Why should we use if-elif-elif...  instead of if-if-if..., though both ways work?

    print(format(grade_average, ".3f") + ", " + letter)

    cnt += 1        # why do we need to increment cnt?