CS: Arrays and Lists Worksheet

Question 1

A list named scores stores the values [88, 92, 75, 100, 67]. What value is stored at index 2? Explain how you found it.

Accepted Answer

The value at index 2 is 75. With 0-based indexing, index 0 is 88, index 1 is 92, and index 2 is 75.

Question 2

A list named colors starts as ["red", "blue", "green", "yellow"]. After the statement colors[1] = "purple", what is the list?

Accepted Answer

The list becomes ["red", "purple", "green", "yellow"]. The value at index 1, which was "blue", is replaced by "purple".

Question 3

A program has the list nums = [4, 8, 15, 16, 23, 42]. Write the value of nums[0] + nums[5] and explain your answer.

Accepted Answer

The value is 46. nums[0] is 4 and nums[5] is 42, so 4 + 42 = 46.

Question 4

A list named names contains 6 elements. What are the valid index values for this list if the language uses 0-based indexing?

Accepted Answer

The valid index values are 0, 1, 2, 3, 4, and 5. A list with 6 elements starts at index 0 and ends at index 5.

Question 5

Explain the difference between an array and a list in many programming languages. Include one example of when a list may be easier to use.

Accepted Answer

An array often has a fixed size and stores values in order, while a list often can grow or shrink as items are added or removed. A list may be easier to use when a program needs to keep adding new user names because the number of names is not known ahead of time.

Question 6

A list starts as [10, 20, 30]. A program appends 40 to the list. What is the list after the append operation?

Accepted Answer

The list becomes [10, 20, 30, 40]. Appending adds the new value to the end of the list.

Question 7

A list named letters starts as ["a", "b", "c", "d"]. A program removes the element at index 2. What is the list after the removal?

Accepted Answer

The list becomes ["a", "b", "d"]. The element at index 2 is "c", so it is removed and the later elements shift left.

Question 8

Trace this loop and write the final value of total: nums = [3, 5, 2, 10]; total = 0; for each n in nums: total = total + n.

Accepted Answer

The final value of total is 20. The loop adds 3, then 5, then 2, then 10, so total is 3 + 5 + 2 + 10 = 20.

Question 9

Write pseudocode that prints every element in the list temperatures = [72, 68, 75, 70].

Accepted Answer

One correct answer is: for each temp in temperatures, print temp. This loop visits each element of the list and prints it one at a time.

Question 10

A list named values is [9, 1, 6, 3]. Write pseudocode to find the largest value in the list.

Accepted Answer

One correct answer is: set largest to values[0]; for each value in values, if value is greater than largest, set largest to value; after the loop, largest is the greatest value. For this list, the largest value is 9.

Question 11

A program tries to access items[10] when items has length 10. Explain the error.

Accepted Answer

This causes an index out of range error in a 0-based list. If the length is 10, the valid indexes are 0 through 9, so index 10 is not valid.

Question 12

A list of test scores is [80, 95, 70, 100, 85]. Write pseudocode to count how many scores are at least 90.

Accepted Answer

One correct answer is: set count to 0; for each score in the list, if score is greater than or equal to 90, add 1 to count; after the loop, count is the number of scores at least 90. For this list, count is 2 because 95 and 100 are at least 90.

CS: Arrays and Lists

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