Kotlin readLine(): getting value from a user

Reading data from user in Kotlin

So far, we have seen how to declare variables and print variables back to user but how do we get input from users?

• Kotlin has readline() function which returns a line from standard input stream.
• readLine() returns String which can be converted to other types as required.

Let us look at readLine() function by taking some examples:

// Code: val msg = readLine() println("Your msg = $msg")

// Output: Hi Your msg = Hi

Here, we ask user to enter a message and then promptly display back the same message.

Getting integer or other data types from readLine() method

• The output returned by readLine() function is String and can be converted to other types.
• We will learn more about type conversion in our section on data types and conversion.
• In the meanwhile, here's how you can convert String returned by readLine() to an Integer.

// Code: println("Enter number 1: ") val x = readLine()!!.toInt() println("Enter number 2: ") val y = readLine()!!.toInt() val sum = x + y println("Sum = $sum")

// Output: Enter number 1: 5 Enter number 2: 3 Sum = 8

• If you examine the code carefully, you'd find another operator !!, the double exclamation operator.
• This operator is part of null pointer safely offered by Kotlin.
• Here, if the output of readLine() is null, instead of calling toInt() on null, the code will fail when met with !! operator.

Note: readLine() may return null if input is redirected to a file and end of file is reached.