A Beginner’s Guide to Kotlin: Variables, Basic Types, Collections, and Control Flow

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A Beginner’s Guide to Kotlin: Variables, Basic Types, Collections, and Control Flow

Kotlin is a modern programming language that is concise, expressive, and fully interoperable with Java. In this blog post, we will go through the fundamentals of Kotlin, including variables, basic types, collections, and control flow. This will help you get started on your Kotlin journey with a strong foundation.

1. Hello, Kotlin!

Let’s start with a simple “Hello, World!” program in Kotlin.

fun main() {
    println("Hello, world!")
}

fun main() {

println("Hello, world!")

}

This is a basic Kotlin program where:

fun is used to declare a function.
main() is the entry point for your program.
println() prints output to the console.

You can see that Kotlin does not require an explicit declaration of a main class or any boilerplate code, making it simple and efficient.

2. Variables in Kotlin

Variables store data in your program, and Kotlin offers two ways to declare variables:

Read-only variables with val
Mutable variables with var

Here’s an example:

fun main() {
    val popcorn = 5 // Read-only variable
    val hotdog = 7   // Read-only variable
    var customers = 10 // Mutable variable
    
    // Some customers leave the queue
    customers = 8
    
    println(customers) // Output: 8
}

fun main() {

val popcorn = 5 // Read-only variable

val hotdog = 7 // Read-only variable

var customers = 10 // Mutable variable

// Some customers leave the queue

customers = 8

println(customers) // Output: 8

}

val stands for value, and it means the variable cannot be reassigned.
var means the variable can be modified.

3. String Templates

In Kotlin, you can easily print the values of variables using string templates. A string template is a way to insert variables or expressions inside a string using the $ symbol.

fun main() {
    val customers = 10
    println("There are $customers customers") // Output: There are 10 customers
    println("There are ${customers + 1} customers") // Output: There are 11 customers
}

fun main() {

val customers = 10

println("There are $customers customers") // Output: There are 10 customers

println("There are ${customers + 1} customers") // Output: There are 11 customers

}

This feature allows you to integrate variables directly into strings, making the code cleaner and more readable.

4. Basic Types in Kotlin

Kotlin supports various basic data types such as:

Integers (Byte, Short, Int, Long)
Floating-point numbers (Float, Double)
Booleans (Boolean)
Characters (Char)
Strings (String)

Example:

fun main() {
    val year: Int = 2020
    val price: Double = 19.99
    val isEnabled: Boolean = true
    val separator: Char = ','
    val message: String = "Hello, world!"
    
    println(year)
    println(price)
    println(isEnabled)
    println(separator)
    println(message)
}

fun main() {

val year: Int = 2020

val price: Double = 19.99

val isEnabled: Boolean = true

val separator: Char = ','

val message: String = "Hello, world!"

println(year)

println(price)

println(isEnabled)

println(separator)

println(message)

}

In Kotlin, you can also rely on type inference, where the compiler automatically infers the type based on the value you assign to a variable.

5. Collections in Kotlin

Kotlin provides several types of collections, such as:

Lists: Ordered collections, can contain duplicates.
Sets: Unordered collections, no duplicates allowed.
Maps: Key-value pairs, where each key is unique.

Here’s how you can use collections:

fun main() {
    // Read-only List
    val shapes = listOf("triangle", "square", "circle")
    println(shapes) // Output: [triangle, square, circle]
    
    // Mutable List
    val mutableShapes = mutableListOf("triangle", "square", "circle")
    mutableShapes.add("pentagon")
    println(mutableShapes) // Output: [triangle, square, circle, pentagon]
}

fun main() {

// Read-only List

val shapes = listOf("triangle", "square", "circle")

println(shapes) // Output: [triangle, square, circle]

// Mutable List

val mutableShapes = mutableListOf("triangle", "square", "circle")

mutableShapes.add("pentagon")

println(mutableShapes) // Output: [triangle, square, circle, pentagon]

}

Sets, unlike lists, do not allow duplicate elements, and maps allow you to associate keys with values.

6. Control Flow in Kotlin

Control flow structures allow you to make decisions and repeat tasks in your programs. Kotlin provides several control flow statements, such as if, when, for, and while.

For example, using if and when:

fun main() {
    val x = 5
    if (x &gt; 0) {
        println("x is positive")
    } else {
        println("x is negative")
    }
    
    val color = "red"
    when (color) {
        "red" -&gt; println("Stop")
        "yellow" -&gt; println("Caution")
        "green" -&gt; println("Go")
        else -&gt; println("Invalid color")
    }
}

fun main() {

val x = 5

if (x > 0) {

println("x is positive")

} else {

println("x is negative")

}

val color = "red"

when (color) {

"red" -> println("Stop")

"yellow" -> println("Caution")

"green" -> println("Go")

else -> println("Invalid color")

}

The if statement checks if a condition is true or false.
The when statement is similar to switch in other languages and helps you handle multiple conditions more efficiently.

Conclusion

In this blog, we’ve covered the basics of Kotlin programming, including variables, basic types, collections, and control flow. Kotlin offers a modern approach to programming that makes writing code clean, concise, and expressive. Whether you’re building Android apps or server-side applications, Kotlin is a versatile language that can help you write better code.

Next Steps

Practice: Try out the exercises mentioned in this post to deepen your understanding.
Explore more: Dive deeper into Kotlin’s powerful features like null safety, extension functions, and coroutines.
Kotlin Documentation: Refer to the official Kotlin documentation for more details on these topics.

Happy coding!