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Your First Kotlin Program

Ayesha
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Your First Kotlin Program

Video Explanationโ€‹

Hello, World!โ€‹

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 Downโ€‹

funโ€‹

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

main()โ€‹

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

println()โ€‹

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

Variations of the Main Functionโ€‹

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

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

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 Templatesโ€‹

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 Kotlinโ€‹

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 Programโ€‹

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 Avoidโ€‹

MistakeWrongCorrect
Missing parenthesesprintln "Hello"println("Hello")
Wrong function keywordfunction main()fun main()
Case sensitivityMain()main()
Missing quotesprintln(Hello)println("Hello")

Summaryโ€‹

  • 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.
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