Your First Kotlin Program

Jun 23, 2026Trushi Jasani

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Your First Kotlin Program

Hello, World!

Every programming journey begins with a simple "Hello, World!" program. In Kotlin, it takes just two lines.

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

Output:

Hello, World!

Breaking It Down

fun

The fun keyword is used to declare a function in Kotlin.

main()

main is the entry point of every Kotlin program. When you run your program, Kotlin starts execution from the main function.

println()

println stands for "print line." It prints the given text to the console followed by a newline character.

Variations of the Main Function

// Basic main function
fun main() {
    println("Hello!")
}

// Main with command-line arguments
fun main(args: Array<String>) {
    println("Arguments: ${args.size}")
}

Print vs Println

fun main() {
    print("Hello, ")      // Does NOT move to next line
    print("World!")       // Continues on the same line
    println()             // Prints a blank new line
    println("Kotlin!")    // Prints and moves to next line
}

Output:

Hello, World!
Kotlin!

Printing Variables

fun main() {
    val name = "Kotlin"
    val version = 2.0

    println("Language: $name")
    println("Version: $version")
    println("Welcome to $name $version!")
}

Output:

Language: Kotlin
Version: 2.0
Welcome to Kotlin 2.0!

String Templates

Kotlin supports string templates using $ for variables and ${} for expressions:

fun main() {
    val a = 10
    val b = 20
    println("Sum of $a and $b is ${a + b}")
}

Output:

Sum of 10 and 20 is 30

Comments in Kotlin

fun main() {
    // This is a single-line comment

    /*
     * This is a
     * multi-line comment
     */

    println("Comments don't affect output") // inline comment
}

Your First Complete Program

fun main() {
    // Greet the user
    val language = "Kotlin"
    val year = 2024

    println("============================")
    println("  Welcome to $language!")
    println("  Year: $year")
    println("============================")
}

Output:

============================
  Welcome to Kotlin!
  Year: 2024
============================

Common Mistakes to Avoid

Mistake	Wrong	Correct
Missing parentheses	println "Hello"	println("Hello")
Wrong function keyword	function main()	fun main()
Case sensitivity	Main()	main()
Missing quotes	println(Hello)	println("Hello")

Summary

• Use fun main() as the program entry point.
• Use println() to print output with a new line.
• Use print() to print without moving to the next line.
• Use $variable or ${expression} inside strings for templates.
• Comments use // for single-line and /* */ for multi-line.