until Range in Kotlin

Introduction

until Range is a fundamental concept every Kotlin developer should understand. Ranges represent intervals of values and integrate cleanly with for loops, contains checks, and filtering operations.

Until creates range excluding end value. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• until creates range excluding end value.
• Equivalent to half-open interval.
• Useful when end index should not be included.

Syntax

for (i in 0 until 5) { }

until Range in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    for (i in 0 until 5) {
        print("$i ")
    }
}

Sample Output

0 1 2 3 4

When to use

Use ranges in for loops, membership tests, and slicing operations on collections or progress indicators.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. Until creates range excluding end value.

3. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Understand the core idea: until creates range excluding end value.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• until creates range excluding end value.
• Equivalent to half-open interval.
• Useful when end index should not be included.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.