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LESSON 1 OF 414 · WELCOME TO SCALA

Printing to the Console in Scala: println and print

Lesson Read the full explanation

TL ; DR:

  • The console is a panel that displays important messages, like errors, for developers.


  • In Scala, we use the println() function to print something to the console. For example, this program:

    println(13)

    prints 13 to the console.


Full lesson:

The console is a panel that displays important messages, like errors, for developers.

Much of the work the computer does with our code is invisible to us by default. If we want to see things appear on our screen, we can print to our console directly.

println():

In Scala, we use the println() function to print something to the console. For example, this program:

println(13)

prints 13 to the console.

When you run this program, this is what you'll see in your console:

13

We refer to the data printed to the console as the output of the program.

Newline character:

Where does the line break after 13 in our program's output come from?

It's important to know that the println() function also prints an invisible newline character after the value we provide.

This newline character inserts a new line in the console. It's like pressing Enter in your text editor to move the cursor to the next line.

This means that if we use println() multiple times, the values will be printed on separate lines in the console:

println(1)
println(2)
println(3)

The ouput of this program would be:

1
2
3

Assignment
Follow the Coding Tutorial and let's print some values to the console!

Hint
Look at the examples above if you get stuck.

STEP 1 OF 1
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    SCALA · WELCOME TO SCALA

    Print in Scala, explained

    What printing is for

    The console is the place where a program shows text to the person running it. Most of the work a program does is invisible: values are computed and stored, but nothing appears on the screen unless the code asks for it. Printing is how you look inside your program, whether to show a result or to check what a variable holds while you debug.

    The text a program writes to the console is called its output.

    println

    In Scala, println prints a value and then moves to a new line. This program:

    println(13)

    produces this output:

    13

    The value goes inside the parentheses. A number is written without quotes, and println prints it as it is. Text goes in double quotes, and the quotes are not printed:

    println("Hello world")

    Hello world

    The newline

    After printing its value, println writes a newline character. It is invisible, and it acts like pressing Enter: the next output starts on a fresh line. That is why several calls produce several lines:

    println(1)
println(2)
println(3)

    1
2
3

    The newline comes after the value, so the output of println(13) is the characters 13 followed by a line break. Nothing is printed before the value.

    print: no newline

    The name print works the same way but without the newline, so the next output continues on the same line:

    print("a")
print("b")
println()

    ab

    The last line, println() with nothing inside, prints only a newline. It ends the line that print left open.

    Numbers and text are different

    The quotes decide what a value is. 1998 is a number and "1998" is text made of four characters. Both print the same way, but they behave differently once you start combining them:

    println(1 + 2)
println("1" + "2")

    3
12

    Adding two numbers does arithmetic, while + between two pieces of text joins them.

    Printing more than one thing

    A single println call prints one value, but text can be joined with + to make one longer value:

    println("Hello" + " " + "world")

    Hello world

    Inside a string, \n is an escape sequence that stands for a newline, so one call can produce two lines:

    println("a\nb")

    a
b

    Common mistakes

    • Missing parentheses. The value goes inside parentheses, and every opening parenthesis needs a closing one.
    • Quotes around a number you want as a number. println("1998") prints the same characters, but the value is text, so it won't take part in arithmetic.
    • Misspelling the name. Scala is case-sensitive: Println and printLn are not println. The compiler reports that the name was not found.
    • Expecting print to start a new line. It doesn't; use println when each value should be on its own line.

    The exercise

    The task is to print the number 1998. Write the call with the number inside the parentheses and no quotes:

    println(1998)

    Run it in the editor above, and the console shows 1998.

    Key takeaways

    • println(value) prints the value and then a newline.
    • Several println calls produce several lines.
    • print(value) prints without the newline.
    • Numbers are written bare; text goes in double quotes, which are not printed.
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