Input/Output (IO) in Kotlin

Input

The function readLine() in Kotlin is a function included in the standard library that allows reading a line of text from the console. It returns the read line as a string.

fun main() {
    println("Enter your name: ")    // A request to enter data will initially be displayed here
    val name = readLine()           // The entered value is read in and assigned to the “name” variable
    println("Hello $name!")         // Output of the result
}

With the help of other special functions such as toInt(), toDouble() or toFloat(), the inputs that are read in as a string can be converted into other data types in order to be processed accordingly later in the program. Below are three examples just to make the principle of operation understandable. Later these functions will be explained in detail and sufficiently practiced.

Entering a number from the console:

fun main() {
    println("Enter a number:")
    val numberValue = readLine()?.toInt()  // Einlesen von Eingaben als String und die Umwandlung in eine Ganzzahl (Int)
    println("The number entered is $numberValue.")
}

Entering a float value from the console:

fun main() {
    println("Enter a float value:")
    val floatValue = readLine()?.toFloat()   // Einlesen von Eingaben als String und die Umwandlung in eine Gleitkommazahl (Float)
    println("The entered float value is $floatValue.")
}

Entering a Double value from the console:

fun main() {
    println("Enter a double value:")
    val doubleValue = readLine()?.toDouble()   // Einlesen von Eingaben als String und die Umwandlung in eine Gleitkommazahl (Double)
    println("The entered double value is $doubleValue.")
}

Output

In Kotlin there are two functions to output data to the console: print() and println() (This function has already been used several times in the previous chapters 🙂 ). These two functions take an object to print to the console, usually a string.

The difference between print() and println() is that the print() function prints the passed text to the console, without Add a line break at the end. However, if you println() If you use this function, it will automatically add a line break to the end of the output. Below are some examples:

fun main() {
    print("Hello ") // Kein Zeilenumbruch
    print("World!") // Kein Zeilenumbruch
    println()       // Wenn man die Funktion ohne Argument benutzt, wird lediglich ein Zeilenumbruch hinzugefügt
    println("Hello ")  // Mit Zeilenumbruch
    println("World!")  // Mit Zeilenumbruch
}

Exercises for this chapter →