"""
# This file is unit01_loop_structure.py. It contains a sample loop that
# calculates the sum of the squares of the numbers 1 through 10.

# George Gollin, University of Illinois, January 15, 2017
"""

# initialize variables here. take note of the names.

# the "accumulator variable" is where we sum the effects of whatever we 
# calculated during successive passes through the loop. we initialize it to 
# zero.  I am using the decimal point to make it a floating point variable, 
# which isn't really necessary.

accumulator = 0.0

# the "increment variable" is something we'll generally need to calculate each
# pass through the loop. after we calculate it we will add it to the accumulator
# variable. Since it will vary each time we go through the loop we don't need
# to initialize it here.

# specify the lower and upper limits for the loop now. Use the range function,
# which takes two integers as arguments, and creates a sequence of unity-spaced
# numbers. Note that the upper limit is not included in the sequence:
# range(1,5) gives the numbers 1, 2, 3, 4. Note that I will add 1 to the upper 
# limit in my range function since range will stop short of this by 1.

lower_limit = 1
upper_limit = 10

# here's the loop. note the "whitespace" that is required, as well as the end-
# of line colon.

for index in range(lower_limit, upper_limit + 1):

    # in python we square things using a double asterisk followed by the 
    # desired power. Note that a carat will not work: 3^2 is NOT 9.
    increment = index ** 2
    
    # now add into the accumulator.
    accumulator = accumulator + increment
    
    # I could have written all of this much more compactly using the +=
    # operator, but that'd be confusing, and you might find that it makes for 
    # buggy, unclear code. 
    
# we end the loop by having a line of unindented code.
    
print("all done! sum of squares is ", accumulator)

###################################################################

"""
Note that I could have written the code more compactly in a single line, but it 
would have been harder to decipher:

   >> print(sum(np.array(range(1,11))**2))
      385
"""