withIndex and zip in Kotlin

val fruits = mutableListOf("apple", "kiwi", "plum")
val prices = mutableListOf(3, 1, 2)

for ((i, fruit) in fruits.withIndex()) {
    println("${i + 1}. $fruit")    // 1. apple, then 2. kiwi, then 3. plum
}

for ((fruit, price) in fruits.zip(prices)) {
    println("$fruit $price")       // apple 3, then kiwi 1, then plum 2
}

Full lesson:

You have looped with for (i in 0 until meals.size). Then meals[i] gave the item. Kotlin has a shorter way to get both.

withIndex() gives each item together with its index. The loop unpacks the two, as val (name, age) = pet unpacks a pair.

for ((i, meal) in meals.withIndex()) {
    println("$i $meal")
}

The index comes first. It starts at 0, so print i + 1 for a numbered list.

a.zip(b) walks two lists side by side. It pairs the first item of a with the first item of b. Then it pairs the second items, and so on. The result is a list of Pairs.

for ((fruit, price) in fruits.zip(prices)) {
    println("$fruit costs $price")
}

zip stops at the end of the shorter list. The extra items are skipped, with no error.

The two work together. fruits.zip(prices).withIndex() gives an index and a pair each time.

Watch out here. A for line can't unpack a pair inside a pair. Unpack the pair on the loop's first line instead.

for ((i, pair) in fruits.zip(prices).withIndex()) {
    val (fruit, price) = pair
    println("${i + 1}. $fruit costs $price")
}

Your task

A quiz show keeps its players in the list players. Their points are in scores, in the same order.

First, print the players as a numbered list from 1, like 1. Ana. Use withIndex().

Then print each player with their points, like Ana has 12 points. Use zip.

Expected output:

1. Ana
2. Ben
3. Cleo
Ana has 12 points
Ben has 9 points
Cleo has 15 points