Real World Example · Variables in Kotlin | Kotlin

Real World Example

A Food Delivery Cart

In a Zomato-style cart, some data never changes during the session (restaurant name, fees set by the app) and some changes on every tap (quantity, total). Choosing const, val and var correctly documents that intent.

Example

The cart total updates as the user adds items.

const val DELIVERY_FEE = 40
const val FREE_DELIVERY_ABOVE = 499

fun main() {
    val restaurant = "Behrouz Biryani"   // fixed for this cart
    val itemPrice = 289                  // fixed per item
    var quantity = 1                     // changes when user taps +

    var total = itemPrice * quantity
    println("$restaurant: $quantity item(s), subtotal ₹$total")

    quantity += 1                        // user taps +
    total = itemPrice * quantity
    val fee = if (total >= FREE_DELIVERY_ABOVE) 0 else DELIVERY_FEE
    println("$restaurant: $quantity item(s), subtotal ₹$total, delivery ₹$fee")
    println("Grand total: ₹${total + fee}")
}

Output

Behrouz Biryani: 1 item(s), subtotal ₹289
Behrouz Biryani: 2 item(s), subtotal ₹578, delivery ₹0
Grand total: ₹578

Practice

Exercise: Create a constant MAX_PIN_ATTEMPTS = 3, a read-only bankName, and a mutable attemptsLeft. Decrease attemptsLeft once and print SBI: 2 attempts left.

Show answer

const val MAX_PIN_ATTEMPTS = 3

fun main() {
    val bankName = "SBI"
    var attemptsLeft = MAX_PIN_ATTEMPTS
    attemptsLeft--
    println("$bankName: $attemptsLeft attempts left")
}