Nested Loop

You can place a loop inside another loop to create a nested loop. The inner loop runs completely for each iteration of the outer loop.

for (i in 1..2) {
    for (j in 1..3) {
        println("i=$i, j=$j")
    }
}
// Output:
// i=1, j=1
// i=1, j=2
// i=1, j=3
// i=2, j=1
// i=2, j=2
// i=2, j=3

When i is 1, the inner loop runs three times (j goes from 1 to 3). Then i becomes 2, and the inner loop runs three more times. This gives us 2 × 3 = 6 total iterations.

Nested loops are commonly used to create patterns or work with grid-like structures:

for (row in 1..3) {
    for (col in 1..row) {
        print("*")
    }
    println()
}
// Output:
// *
// **
// ***

Here, the inner loop's range depends on the outer loop's variable, creating a triangle pattern. The print() function outputs without a newline, while println() moves to the next line after each row.