Standard input in Kotlin

Standard input

Standard input is a stream of data that goes into the program. By default, standard input gets data from the keyboard but it is possible to get it from a file.

• Kotlin functions
• Kotlin has a useful function to read data from the standard input. It is supported by the operating system. It is readline. It reads the whole line as a string.

 fun main() {
    val line = readLine()!!
    println(line)
 }

• If you need to get a number from the input, you can use this construction:

 fun main() {
    val line = readLine()?.toInt()!!
    println(line)
 }

• To accept multiple words in a single use the following code

 val (a, b) = readLine()!!.split(' ')
 println("$a, $b")
 val (c, d, e) = readLine()!!.split(' ')
 println("$c, $d, $e")

• Java Scanner
• Another way to obtain data from the standard input is to use the Java Scanner.
• Scanner allows a program to read values of different types (strings, numbers, etc) from the standard input.
• You can use any method to add Scanner to your program.

 val scanner = Scanner(System.`in`)

• Scanner.next() reads only one word, not a line. If the user enters Hello, Kotlin, it will read Hello,
• It's possible to read a number as a string using scanner.next() or scanner.nextLine() methods, if the number is on a new line.

 fun main() {
    val scanner = Scanner(System.`in`)
    val line = scanner.nextLine()
    val number = scanner.nextInt()
    val string = scanner.next()
    println(line)
    println(number)
    println(string)
 }

• Also, the Scanner type provides several methods (functions) for reading values of other types. Read Class Scanner.

Invoking functions

• A function is a sequence of instructions, we can invoke it from a program by calling its name.
• Functions arguments
• When we want to use a function, we can invoke (or call) it using its name followed by parentheses.
• If a function takes one or more arguments (input data), they should be passed in the parentheses. 
• Producing a result
• Some functions not only take arguments but also produce (return) some results.
• All functions return a result, even the println function. The result is a special value called Unit that practically means no result.

Do's and Don'ts

• Scanner.next() reads only one word, not a line. If the user enters Hello, Kotlin, it will read Hello,