Range

Learn ranges with 1..10 and until/downTo.

Range

A range is a sequence of numbers. 1..5 contains all numbers from 1 to 5 (5 inclusive). until excludes the upper bound.

for (i in 1..5) print(i)      // 12345
for (i in 1 until 5) print(i) // 1234
for (i in 5 downTo 1) print(i) // 54321

1..5 includes 5, 1 until 5 does not. downTo counts backward. Ranges are especially useful in for loops.

Two dots (..) make a range; both ends are inclusive.

Exercise Count forward and backward

Write a fun main(). Use for (i in 1..5) { println(i) } to count 1 to 5. Then use for (i in 5 downTo 1) { println(i) } to count 5 to 1 backward. Write both loops.

Show example solution

fun main() {
    for (i in 1..5) {
        println(i)
    }
    for (i in 5 downTo 1) {
        println(i)
    }
}

Step size

step sets the range's step size. The default step is 1; step 2 jumps by two each time.

for (i in 1..10 step 2) print(i)  // 13579
for (i in 10 downTo 1 step 3) print(i) // 10741

The first loop prints 1, 3, 5, 7, 9. The second counts down from 10 to 1 by threes: 10, 7, 4, 1.

step works with both .. and downTo; the step is always a positive integer.

Test yourself

Match the range forms

1..5

1,2,3,4,5
1 until 5

1,2,3,4
5 downTo 1

5,4,3,2,1
1..1

1

Complete the range with until

for (i in 1 ____ 5) { println(i) }

Show answer

for (i in 1 until 5) { println(i) }

Which numbers does 1 until 5 contain?
- 1,2,3,4,5
- 5
- 1,2,3
- 1,2,3,4
Show answer

1,2,3,4 — until excludes the upper bound: 1, 2, 3, 4.

Next lesson: break and continue

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