Can you describe the concept of side effects in programming and give examples?

Side effects in programming are any changes in state that occur outside the local scope of a function or method, or interactions with the external world, beyond returning a value. These include, for example, changing global variables, writing to a file, modifying a database, outputting to the screen, sending network requests.

Example:

var counter = 0

fun increment() {
    counter += 1  // changing external state — side effect
}

fun sum(a: Int, b: Int): Int {
    return a + b  // no side effects, pure function
}

In Android, side effects are often related to updating the UI, saving data, or calling APIs. Managing side effects is important for code predictability and testability.