Looping through an array by index
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which loop visits every index of the list scores?
2. A list arr has 5 elements. Which values does i take in: for i in range(len(arr)):
3. Which code adds up every element of arr into total?
4. Which line finds the largest element so far inside the loop?
5. Which code doubles every element of arr in place?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1for i in range(len(arr)): | ALoops i through every index of arr, from 0 to the last position | |
| 2arr[i] = arr[i] * 2 | Brange() needs a number, but arr is a list. It should be range(len(arr)) so i covers every index. | |
| 3Totalling array elements: start a total at 0, then add arr[i] on every pass | Clargest = arr[0] for i in range(len(arr)): if arr[i] > largest: largest = arr[i] | |
| 4Finding the largest element: start with the first element and replace it whenever arr[i] is bigger | DAdds the index i instead of the element arr[i], so the total is of positions, not values. It should be total = total + arr[i]. | |
| 5for i in range(len(arr)): total = total + i | Etotal = 0 for i in range(len(arr)): total = total + arr[i] | |
| 6for i in range(arr): arr[i] = arr[i] + 1 | FChanges the element at position i in place by doubling it |
C
Definitions
for i in range(len(arr)):
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
for i in _____(len(arr)):
2.
total = 0
for i in range(___(arr)):
total = total + arr[i]
3.
largest = arr[0]
for i in range(len(arr)):
if arr[i] _ largest: largest = arr[i]
4.
for i in range(len(arr)):
arr[_] = arr[i] * 2
5.
total = 0
for i in range(len(arr)):
total __ arr[i]
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
scores = [12, 8, 15, 9]
B
total = 1
C
for i in range(len(scores)):
D
total = total + scores[i]
E
print(total)
Question 2
A
marks = [56, 91, 73, 84]
B
biggest = marks(0)
C
for i in range(len(marks)):
D
if marks[i] > biggest:
E
biggest = marks[i]
Question 3
A
prices = [10, 20, 30]
B
for i in range(prices):
C
prices[i] = prices[i] * 2
D
print(prices)
Question 4
A
temps = [21, 25, 19, 30]
B
total = 0
C
for i in range(len(temps)):
D
total = total + i
E
average = total / len(temps)
Question 5
A
nums = [4, 9, 2, 7]
B
for i in range(len(nums)):
C
nums = nums[i] + 1
D
print(nums)
Answer Key
Looping through an array by index
Section A: Quick Questions
Q1
B — for i in range(len(scores)):
Q2
A — 0, 1, 2, 3, 4
Q3
B — for i in range(len(arr)):
total = total + arr[i]
Q4
A — if arr[i] > largest:
Q5
A — for i in range(len(arr)):
arr[i] = arr[i] * 2
Section B: Match the Pairs
Q1
for i in range(len(arr)): → Loops i through every index of arr, from 0 to the last position
Q2
arr[i] = arr[i] * 2 → Changes the element at position i in place by doubling it
Q3
Totalling array elements: start a total at 0, then add arr[i] on every pass → total = 0
for i in range(len(arr)):
total = total + arr[i]
Q4
Finding the largest element: start with the first element and replace it whenever arr[i] is bigger → largest = arr[0]
for i in range(len(arr)):
if arr[i] > largest:
largest = arr[i]
Q5
for i in range(len(arr)):
total = total + i → Adds the index i instead of the element arr[i], so the total is of positions, not values. It should be total = total + arr[i].
Q6
for i in range(arr):
arr[i] = arr[i] + 1 → range() needs a number, but arr is a list. It should be range(len(arr)) so i covers every index.
Section C: Definitions
Q1
for i in range(len(arr)): — Loops i through every index of arr, so arr[i] can be read or changed and you know each element's position. Used for totals, finding the largest value and editing in place.Section D: Fill in the Blanks
Q1
for i in range(len(arr)):Q2
total = 0
for i in range(len(arr)):
total = total + arr[i]Q3
largest = arr[0]
for i in range(len(arr)):
if arr[i] > largest: largest = arr[i]Q4
for i in range(len(arr)):
arr[i] = arr[i] * 2Q5
total = 0
for i in range(len(arr)):
total += arr[i]Section E: Spot the Error
Q1
B — A running total must start at 0. Starting at 1 adds an extra 1 to the answer. It should be total = 0.
Q2
B — Array elements are read with square brackets, not round ones. Round brackets try to call marks as a function. It should be biggest = marks[0].
Q3
B — range() needs a whole number, but prices is a list. Use len(prices) to get the number of elements: for i in range(len(prices)):
Q4
D — i is the index (position), not the element. Adding i totals 0, 1, 2, 3 instead of the temperatures. It should be total = total + temps[i].
Q5
C — This replaces the whole array with a single number. To change one element in place, assign to nums[i]. It should be nums[i] = nums[i] + 1.