Level 15. Counting Loops

What if you want to do something and know which round you’re on? That’s what for is for!

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

This prints:

1
2
3
4
5

The variable i counts from the first number to the last number (both included). Think of it as: “for every number i from 1 to 5, do this.”

The range ..

The two dots .. mean “from here to there”:

FizzBuzz with a for loop

Remember FizzBuzz? Now we can do the real version. Loop through all the numbers!

fun fizzbuzz(n) =>
  if n % 15 == 0 { "fizzbuzz" }
  else if n % 3 == 0 { "fizz" }
  else if n % 5 == 0 { "buzz" }
  else { show(n) }

fun main() {
  for i in 1..100 {
    println(fizzbuzz(i))
  }
}

Notice show(n) in the last branch. It turns a number into a string (so show(7) gives "7"). We need it because every branch must return the same type, and the other branches already return strings.

That’s only 10 lines of code and it prints all 100 fizzbuzz results!

Using the loop variable

The loop variable is a regular integer. You can do math with it:

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

This prints the squares: 1, 4, 9, 16, 25.

🎯 Try it: Use a for loop to print the first 10 multiples of 7 (7, 14, 21, …).

🎯 Try it: Print a countdown: for i in 1..5 { println(6 - i) }. What numbers do you get?