Repeat work with for-in

A teacher wants to total several scores. A for-in loop visits each element of a sequence and performs the body for that element. It lets you describe one calculation without duplicating it for every student.

The loop variable receives the next element on each iteration. A running total stores state across iterations. Ranges such as 1...3 include their upper bound, while 0..<3 exclude it. Nested loops perform the inner sequence for each outer iteration, so their total work can multiply.

Save this complete program as main.swift and run it with the Swift toolchain. No separate input file is needed.

Swift · complete program

let scores = [70, 80, 90]
var total = 0
for score in scores {
  total += score
}
print(total)

Expected output

240

Follow the execution

Total starts at zero, becomes 70, then 150, then 240. The print lies outside the loop, so it displays the finished total once. Moving it inside would display intermediate totals instead.

Try this program in the Swift compiler. Paste the complete source above.

Your task: What total results if you append another score of 60?

Swift · complete program

let scores = [70, 80, 90]
var total = 0
for score in scores {
  total += score
}
print(total)

Worked answer

The total becomes 300 because a fourth iteration adds 60 to 240. The loop body needs no extra copy; it follows the collection’s elements.

Use break to leave the loop and continue to skip the rest of one iteration. Neither means “skip the entire program.” Do not mutate a collection’s iteration structure casually; create a deliberate transformation or a separate result when changing its contents.

The total becomes 300 because a fourth iteration adds 60 to 240. The loop body needs no extra copy; it follows the collection’s elements. Use break to leave the loop and continue to skip the rest of one iteration.

Further reading: official Swift language guide.