Chapter 15 - Nested Loop Example

[petersm3]

Don't know if this has already been addressed; logging for completeness

From: Peterson, Matthew
Sent: Tuesday, January 14, 2020 11:07 PM
To: O'Neil, Shawn shawn.oneil@cgrb.oregonstate.edu
Subject: Chapter 15 code question - nested for loop

https://open.oregonstate.education/app/uploads/sites/6/2016/10/II.3_14_nested_loop_illustrated.png

total = 0
sum:int = 0

for i in range(0,4):
    total = total + i
    for j in range(0,3):
        total = total + j + i
        print("total is: " + str(total))
    sum = sum + i

print("Done! Final total is:" + str(total))

What is the line:

sum = sum + i

for, if the variable sum is never referenced? (only the variable 'total' is ever referenced)

Text lists: "We see that both blocks also make use of variables defined outside them; the inner block makes use of sum, i, and j, while lines specific to the outer block make use of sum and i (but not j)."

Referencing your original, hand-written notes, sum is used, (total is never referenced), and the code is different... e.g., there is no line assigning either 'total' or 'sum' to total+i+j OR sum+i+j, respectively.

The below code also produces a different result:

Hand written notes, transcribed:

sum: int = 0
i: int

for i in range(0,4):
    sum = sum + i
    j: int
    for j in range(0,3):
        sum = sum + j
        print("sum is " + str(sum))

    sum = sum + i

print("done")

[petersm3]

In discussion with @oneilsh (in 2020) it was determined that:

"The code in the textbook is incorrect, mixing the variables 'sum' and 'total'"

I rewrote the code (in my class slides) to match the intent of the image shown in the book, which should be independently verified, and the text (inline in the image) potentially corrected.

https://github.com/oneilsh/apcb_second_edition/blob/master/images/part2-03-collections-looping.images/II.3_14_nested_loop_illustrated.png

sum: int = 0
i: int

for i in range(0,4):
    sum = sum + i
    j: int
    for j in range(0,3):
        sum = sum + j
        print("sum is " + str(sum))

    sum = sum + i

print("Done!")