How to use readLine function in Kotlin

Using the readLine Function in Kotlin

The readLine function in Kotlin is used to read a line of text from the standard input. It returns a String?, which means it can be either a string or null.

Handling Null Safety

In your code, you are correctly using the readLine function, but you are not handling the null safety. If the input is null (which means the end of the input has been reached), calling reversed() on it will throw a NullPointerException.

Here's how you can handle it:

fun main(args: Array<String>) {
    // Step 1: Read a line of text from the standard input
    val inputString = readLine()

    // Handle null safety
    if (inputString != null) {
        // TODO: Write a function to reverse the input string
        val reversedString = inputString.reversed()

        // Step 3: Print the reversed string using the println() function
        println(reversedString)
    } else {
        println("No input provided")
    }
}

Alternatively, you can use the safe call operator ?. to avoid the NullPointerException:

fun main(args: Array<String>) {
    // Step 1: Read a line of text from the standard input
    val inputString = readLine()

    // Use safe call operator
    val reversedString = inputString?.reversed()

    // Step 3: Print the reversed string using the println() function
    println(reversedString)
}

Important Caveats

Note that readLine will block until the user enters a line of text and presses enter. If you are running this code in an environment where there is no standard input (e.g., some online code editors), readLine may not work as expected.