Kotlin For Loop
Iterating through ranges and collections
🔄 What is For Loop?
For loop is the most versatile loop in Kotlin, perfect for iterating through ranges, collections, and arrays. It automatically handles the iteration logic, making your code cleaner and more readable than manual counting.
// Basic for loop
for (i in 1..5) {
println("Step $i")
}
For Loop Variations
Range Loop
Iterate through number ranges
for (i in 1..10) {
println(i)
}Collection Loop
Iterate through lists and arrays
val list = listOf("A", "B", "C")
for (item in list) {
println(item)
}Step Loop
Skip numbers with step
for (i in 0..10 step 2) {
println(i) // 0, 2, 4, 6, 8, 10
}Reverse Loop
Count backwards
for (i in 10 downTo 1) {
println(i)
}🔹 Basic Range Loop
Iterate through a range of numbers:
fun main() {
// Print numbers 1 to 5
println("Counting from 1 to 5:")
for (number in 1..5) {
println("Number: $number")
}
// Calculate sum
var sum = 0
for (i in 1..10) {
sum += i
}
println("\nSum of 1 to 10: $sum")
}Output:
Counting from 1 to 5:
Number: 1
Number: 2
Number: 3
Number: 4
Number: 5
Sum of 1 to 10: 55
🔹 Looping Through Collections
Iterate through lists, arrays, and other collections:
fun main() {
val colors = listOf("Red", "Green", "Blue", "Yellow")
val scores = arrayOf(85, 92, 78, 96, 88)
// Loop through list
println("Available colors:")
for (color in colors) {
println("🎨 $color")
}
// Loop through array with processing
println("\nStudent scores:")
for (score in scores) {
val grade = when {
score >= 90 -> "A"
score >= 80 -> "B"
score >= 70 -> "C"
else -> "F"
}
println("Score: $score (Grade: $grade)")
}
}Output:
Available colors:
🎨 Red
🎨 Green
🎨 Blue
🎨 Yellow
Student scores:
Score: 85 (Grade: B)
Score: 92 (Grade: A)
Score: 78 (Grade: C)
Score: 96 (Grade: A)
Score: 88 (Grade: B)
🔹 Loop with Index
Get both the item and its position:
fun main() {
val fruits = listOf("Apple", "Banana", "Orange")
// Using withIndex()
println("Shopping list:")
for ((index, fruit) in fruits.withIndex()) {
println("${index + 1}. $fruit")
}
// Using indices property
println("\nUsing indices:")
for (i in fruits.indices) {
println("Item $i: ${fruits[i]}")
}
// Manual indexing
println("\nManual counting:")
var position = 1
for (fruit in fruits) {
println("Position $position: $fruit")
position++
}
}Output:
Shopping list:
1. Apple
2. Banana
3. Orange
Using indices:
Item 0: Apple
Item 1: Banana
Item 2: Orange
Manual counting:
Position 1: Apple
Position 2: Banana
Position 3: Orange
🔹 Step and Reverse Loops
Control the iteration pattern:
fun main() {
// Step loop - skip numbers
println("Even numbers from 0 to 10:")
for (i in 0..10 step 2) {
println(i)
}
// Reverse loop
println("\nCountdown:")
for (i in 5 downTo 1) {
println("$i...")
}
println("🚀 Launch!")
// Reverse with step
println("\nEvery 3rd number backwards:")
for (i in 15 downTo 0 step 3) {
println(i)
}
}Output:
Even numbers from 0 to 10:
0
2
4
6
8
10
Countdown:
5...
4...
3...
2...
1...
🚀 Launch!
Every 3rd number backwards:
15
12
9
6
3
0
🔹 Nested For Loops
Loop inside another loop:
fun main() {
// Multiplication table
println("Multiplication Table (1-5):")
for (i in 1..5) {
for (j in 1..5) {
print("${i * j}\t")
}
println() // New line after each row
}
// Pattern printing
println("\nStar pattern:")
for (row in 1..4) {
for (star in 1..row) {
print("⭐")
}
println()
}
}Output:
Multiplication Table (1-5):
1 2 3 4 5
2 4 6 8 10
3 6 9 12 15
4 8 12 16 20
5 10 15 20 25
Star pattern:
⭐
⭐⭐
⭐⭐⭐
⭐⭐⭐⭐