Kotlin Syntax Basics

A few rules cover most of what Kotlin code looks like.

One statement per line, no semicolons. A semicolon is only needed to put two statements on one line.

Curly braces mark blocks of code:

fun main() {
    if (10 > 5) {
        println("Ten is bigger")
    }
}

Ten is bigger

Conditions go in parentheses: if (10 > 5).

Indentation is four spaces by convention. Kotlin doesn't require it, but it keeps code readable, and IntelliJ formats it for you (Code → Reformat Code).

Case matters. name and Name are different. The conventions: camelCase for variables and functions (firstName, calculateTotal); PascalCase for classes (ShoppingCart); and SCREAMING_SNAKE_CASE for constants (MAX_USERS).

Almost everything is an expression. if, when, and try all produce values you can assign — you'll see this throughout the course.

Common mistakes

• A missing closing brace — the compiler reports something like Missing '}'. Your IDE highlights matching braces to help.
• Putting a line break in the wrong place. Kotlin ends a statement at a line break when it can, so start a continued line with an operator like . or ?: — not end the previous line with +, which also works but is easy to get wrong.