Kotlin Operators and Strings

Operators let you calculate and compare values, and strings let you work with text.

Arithmetic Operators

Operator	Name	Example	Result
`+`	Add	`7 + 3`	`10`
`-`	Subtract	`7 - 3`	`4`
`*`	Multiply	`7 * 3`	`21`
`/`	Divide	`7 / 2`	`3`
`%`	Remainder	`7 % 2`	`1`

When both numbers are Int, division drops the decimal part. Use a Double to keep it:

Example

kotlin

fun main() {
    println(7 / 2)
    println(7.0 / 2)
    println(7 % 2)

    var balance = 500
    balance += 200   // same as balance = balance + 200
    balance -= 50
    println(balance)
    balance++
    println(balance)
}

Output

Comparison and Logical Operators

Comparison operators give a Boolean (true or false):

Operator	Meaning
`==`	equal to
`!=`	not equal to
`>` and `<`	greater than, less than
`>=` and `<=`	greater or equal, less or equal

Logical operators join conditions:

&& (and): true only if both sides are true
|| (or): true if at least one side is true
! (not): turns true into false and false into true

Example

kotlin

fun main() {
    val age = 20
    val hasCnic = true
    println(age >= 18 && hasCnic)
    println(age < 13 || age > 60)
    println(!hasCnic)
}

Output

true
false
false

String Templates

Put a variable inside a string with $. For a calculation or a property, use ${ }:

Example

kotlin

fun main() {
    val item = "Biryani"
    val price = 350
    println("One plate of $item costs Rs $price")
    println("Two plates cost Rs ${price * 2}")
    println("The word $item has ${item.length} letters")
}

Output

One plate of Biryani costs Rs 350
Two plates cost Rs 700
The word Biryani has 7 letters

Useful String Functions

Example

kotlin

fun main() {
    val city = "  Karachi  "
    val clean = city.trim()
    println(clean)
    println(clean.uppercase())
    println(clean.lowercase())
    println(clean.length)
    println(clean[0])
    println(clean.contains("chi"))
    println(clean.startsWith("Ka"))
    println(clean.substring(0, 4))
    println(clean.replace("a", "@"))
}

Output

Karachi
KARACHI
karachi
7
K
true
true
Kara
K@r@chi

Function	What it does
`trim()`	Removes spaces at the start and end
`uppercase()` / `lowercase()`	Changes the case
`length`	Number of characters (a property, no brackets)
`[i]`	The character at position `i` (counting from 0)
`contains()`	Checks whether some text is inside
`substring(a, b)`	Characters from position `a` up to, but not including, `b`
`replace(old, new)`	Replaces text

Strings in Kotlin are immutable: functions like uppercase() return a new string and do not change the original.

Comparing Strings

Use == to check if two strings have the same text. To ignore upper and lower case, use equals with ignoreCase = true:

Example

kotlin

fun main() {
    val a = "pakistan"
    val b = "Pakistan"
    println(a == b)
    println(a.equals(b, ignoreCase = true))
}

Output

false
true

Exercise

What does println(17 % 5) print?

323.412