''' Purpose: deepen variable manipulation understanding.

    Problem: track the number of rabbits over five generations, where
             the number of rabbits doubles each generation. at the start
             there are two rabbits
'''

# first generation
generation  = 1
nbr_rabbits = 2
# print( 'Memory box for generation', id( generation ) )
# id() is a function, gives you the location in your computer of the value of variable (generation)
# you don't need to know this

print( 'Generation: ', generation  )
print( 'Rabbits:    ', nbr_rabbits )

reply = input( 'Enter when ready: ' )           # waits until user enters something

# next generation
generation  = generation + 1   # generation on the right is the old value of generation --> update the variable generation
# new value of generation on the left --> now holds 2 because old generation value is 1
# increment = adding
nbr_rabbits = nbr_rabbits * 2  # doubles the # of rabbits from the last generation
# here we are updating the two variables we had before
# from here on out, generation and nbr_rabbits will have the new values; unless we update them again
# = is the assignment operator: we are assigning values on the right to the variables on the left

print( 'Generation: ', generation  )
print( 'Rabbits:    ', nbr_rabbits )

reply = input( 'Enter when ready: ' )           # waits until user enters something

# next generation
generation  = generation + 1  # old (Right) generation = 2 --> 2 + 1 = 3 (new (Left) generation)
nbr_rabbits = nbr_rabbits * 2 # old (Right) nbr_rabbits = 4 --> 4 * 2 = 8 (new (Left) nbr_rabbits)
# you can update the same variables, it only changes from the point you update onwards
# the old value of the variables are gone; you can't get it back
# when you are assigning values to a variable, you are storing them to that variable

# the ability to update variables can give you the ability to accumulate things
# like finding the total of a group of numbers - we'll get to this soon

print( 'Generation: ', generation  )
print( 'Rabbits:    ', nbr_rabbits )

reply = input( 'Enter when ready: ' )           # waits until user enters something

# next generation
generation  = 4
nbr_rabbits = 16

print( 'Generation: ', generation  )
print( 'Rabbits:    ', nbr_rabbits )

reply = input( 'Enter when ready: ' )           # waits until user enters something

# next generation
generation  = 5
nbr_rabbits = 32

print( 'Generation: ', generation  )
print( 'Rabbits:    ', nbr_rabbits )

# variables can be re-used and updated

# what happens when you have bigger generations? Let the computer to double, instead of doing it manually

# identifier vs variable
#   identifier = name
#       print() is a name for a function
#       generation is a name for a variable
#       syntax rule: has to start with a letter, and can be followed by numbers and other characters; has to be one word
#       style rule: snake_case
#   variable = thing that stores a value in memory

# our programs so far are static - they run the same thing every time
# usually programs want to be interactive - get information from the user and do things with that info
# give output depending on the user's input