How it works
Variables store changing state; lists store ordered collections that algorithms can search, count, filter, or transform.
Track list position, current item, accumulator values, and any changes made inside the loop.
Common error
AP CSP pseudocode list indexing commonly starts with the first item at index 1.
Worked example
Track a list update using one-based AP CSP indexing.
Data / pseudocode
items <- [4, 7, 9]
items[2] <- items[1] + 1
APPEND(items, 12)
DISPLAY(items[2])The first item is at index 1. Replacing item 2 changes the list to [4, 5, 9], and APPEND adds 12 at the end. The displayed value is 5. Do not use Java zero-based indices in this pseudocode.
Exercises
3.2.1
Start with values = [3, 6, 8]. Remove the item at position 1, then insert 5 at position 2. What is the final list?
Show solution
Removing position 1 gives [6, 8]. Inserting 5 at position 2 shifts 8 right, producing [6, 5, 8].
3.2.2
Write pseudocode that counts how many items in values are greater than 10, including an empty list.
Show solution
Solution pseudocode
count <- 0
FOR EACH value IN values {
IF (value > 10) { count <- count + 1 }
}
DISPLAY(count)
An empty list leaves count at 0.