'''lecture_21_while_miles.py
Use a while loop to get mileage from trips. Loop sentinel is a negative milage (invalid entry)
Goal: Compute the total number of miles across all trips and average trip miles
UPDATE 1: Add break statement if sentinel is negative
UPDATE 2: Introduce increment operator
Oliver W. Layton
CS 151: Computational Thinking: Visual Media
Fall 2020
'''
# Declare variables for number of trips that are entered and total miles entered
numTrips = 0
numMiles = 0

# Get user input
milesEnteredByUser = float(input('Please enter your trip mileage (Enter negative number when done) >>>'))

# Get data while the user entry is valid (>0), first updating the mileage total and number of trips
# while True: # "bad" way
while milesEnteredByUser >= 0:  # "Good way"
    # numTrips = numTrips + 1  #1
    # numMiles = numMiles + milesEnteredByUser  #2

    # Using the increment operator:
    numTrips += 1  #1
    numMiles += milesEnteredByUser  #2

    # Also -= decrement operator
    # a = 3
    # a -= 2  # a = a - 2


    # Get user input again
    milesEnteredByUser = float(input('Please enter your trip mileage (Enter negative number when done) >>>'))

    # if milesEnteredByUser < 0:  # Not recommended
    #     break

# Compute the average number of miles across all trips
avgMiles = numMiles / numTrips

# Print number of total miles and total numebr of trips
print('Total number of trips:', numTrips)
print('Total number of miles:', numMiles)

# Print number of average number of miles
print('Average number of miles traveled:', avgMiles)