Count from One to Five

The concept

A for loop repeats a block of code once for each value in a sequence. The most common way to build a numeric sequence in R is with the : operator: 1:5 produces the sequence 1, 2, 3, 4, 5. Written as for (i in 1:n) { ... }, the loop variable i takes on each of those values in turn, running the body once per value. This is far more convenient than writing out five separate cat() calls by hand, and it still works correctly if n changes later.

One subtlety worth knowing: : has higher precedence than + or -. That means 1:n - 1 doesn't mean "from 1 to (n minus 1)" the way it might in ordinary math — R builds 1:n first, then subtracts 1 from every number in that sequence.

Worked example

laps <- 3

for (i in 1:laps) {
  cat("Lap ", i, "\n", sep = "")
}

Lap 1
Lap 2
Lap 3

Here, 1:laps builds the sequence 1, 2, 3, and the loop prints one labeled line per value. Because there's no stray arithmetic mixed into the range, i takes on exactly the values 1, 2, and 3, in that order — nothing shifted.

Your turn

The starter code is meant to loop over 1 through 5, but its range expression has an extra - 1 tacked onto the end. Because : is evaluated before -, that extra subtraction shifts every value in the sequence down by one. Remove the subtraction from the range so the loop counts through the intended numbers.

If something goes wrong

If the printed numbers start at 0 instead of 1, or seem to be missing the highest value, that's the telltale sign of this exact precedence issue — the sequence is being built correctly but then shifted afterward. Try temporarily printing the full range on its own, like cat(1:n - 1) versus cat(1:n), to see the difference directly, then remove whichever piece is producing the shifted sequence.