JuniorTheoryCommon

What happens when this program is compiled and run?

SWIFT

let prices = [10, 20, 30]
let item = prices[prices.count]
print(item)

The program crashes

Expecting 30: taking count for the index of the last element. Indices start at zero, so the last one is count - 1, and index count crashes the program.
Expecting nil: reading by an index gives a plain Int, not an optional like first and last. An index that does not exist stops the program with Index out of range.

JuniorTheoryCommon

SWIFT

let prices = [10, 20, 30]
let item = prices[prices.count]
print(item)

The program crashes

Expecting 30: taking count for the index of the last element. Indices start at zero, so the last one is count - 1, and index count crashes the program.
Expecting nil: reading by an index gives a plain Int, not an optional like first and last. An index that does not exist stops the program with Index out of range.