Data Types & Variables

Mutable Variables

A mutable variable is declared with the var keyword and represents a value that is expected to change throughout a program.

var age = 25
age = 26

Immutable Variables

An immutable variable is declared with the val keyword and represents a value that must remain constant throughout a program.

val goldenRatio = 1.618

Type Inference

When a data type is not specified in a variable declaration, the variable’s data type can be inferred through type inference.

// The following variable is assigned a text value within double quotes, thus the inferred type is String 

var color = "Purple"

String Concatenation

String concatenation is the process of combining Strings using the + operator.

var streetAddress = "123 Main St."
var cityState = "Brooklyn, NY" 

println(streetAddress + " " + cityState) 
// Prints: 123 Main St. Brooklyn, NY

String Templates

String templates contain String values along with variables or expressions preceded by a $ symbol.

var address = "123 Main St. Brooklyn, NY"
println("The address is $address") 
// Prints: The address is 123 Main St. Brooklyn, NY

Built-in Properties and Functions

The Kotlin String and Character data types contain various built-in properties and functions. The length property returns the number of characters in a String, and the capitalize() function capitalizes the first letter of a String.

var monument = "the Statue of Liberty"

println(monument.capitalize()) // Prints: The Statue of Liberty
println(monument.length) // Prints: 21

Character Escape Sequences

Character escape sequences consist of a backslash and character and are used to format text.

\n Inserts a new line
\t Inserts a tab
\r Inserts a carriage return
\' Inserts a single quote
\" Inserts a double quote
\\ Inserts a backslash
\$ Inserts the dollar symbol

print("\"Excellent!\" I cried. \"Elementary,\" said he.") 

// Prints: "Excellent!" I cried. "Elementary," said he.

Arithmetic Operators

The arithmetic operators supported in Kotlin include + addition, - subtraction, * multiplication, / division, and % modulus.

5 + 7  // 12
9 - 2  // 7
8 * 4  // 32
25 / 5 // 5 
31 % 2 // 1

Order of Operations

The order of operations for compound arithmetic expressions is as follows:

Parentheses
Multiplication
Division
Modulus
Addition
Subtraction

When an expression contains operations such as multiplication and division or addition and subtraction side by side, the compiler will evaluate the expression in a left to right order.

5 + 8 * 2 / 4 - 3 // 6 
3 + (4 + 4) / 2   // 7
4 * 2 + 1 * 7     // 15
3 + 18 / 2 * 1    // 12  
6 - 3 % 2 + 2     // 7

Augmented Assignment Operators

An augmented assignment operator includes a single arithmetic and assignment operator used to calculate and reassign a value in one step.

var batteryPercentage = 80

// Long Syntax 
batteryPercentage = batteryPercantage + 10 

// Short Syntax with an Augmented Assignment Operator 
batteryPercentage += 10

Increment and Decrement Operators

Increment and decrement operators provide a shorthand syntax for adding or subtracting 1 from a value. An increment operator consists of two consecutive plus symbols, ++, meanwhile a decrement operator consists of two consecutive minus symbols, --.

var year = 2019 
year++ // 2020
year-- // 2019

The Math Library

The Math library, inherited from Java, contains various mathematical functions that can be used within a Kotlin program.

Math.pow(2.0, 3.0)  // 8.0
Math.min(6, 9)      // 6 
Math.max(10, 12)    // 12
Math.round(13.7)    // 14

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