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LESSON 1 OF 415 · WELCOME TO SWIFT

Printing to the Console in Swift with print()

Lesson Read the full explanation

TL ; DR:

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


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

    print(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.

print():

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

print(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:

It's important to know that the print() 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 print() multiple times, the values will be printed on separate lines in the console:

print(1)
print(2)
print(3)

The output 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
    Ctrl + Enter to check

    SWIFT · WELCOME TO SWIFT

    Print in Swift, explained

    What printing does

    A program does most of its work out of sight. To see a result, you ask the program to show it. In Swift the simplest way is the print() function, which writes a value to the console, the text panel where a running program shows its output and where the compiler reports errors. Whatever a program writes there is its output.

    This program prints a number:

    print(13)

    The console shows:

    13

    You put the value between the parentheses. Swift evaluates it and prints its text form. Numbers, strings, booleans and arrays all work:

    print(42)
print(3.5)
print(true)
print([1, 2, 3])

    42
3.5
true
[1, 2, 3]

    Each call ends the line

    After the value, print() adds an invisible newline character, the same thing that pressing Enter inserts in a text editor. The next piece of output therefore starts on a fresh line, and the cursor does not sit on the line you just wrote. There is no blank line after 13; the newline only ends the line that holds it.

    Because of this, several calls produce several lines:

    print(1)
print(2)
print(3)

    1
2
3

    Calling print() with nothing in the parentheses prints only the newline, which gives you an empty line.

    Printing several values and changing the ending

    You can pass several values, separated by commas. By default print puts a single space between them:

    print(1, 2, 3)
print(1, 2, 3, separator: "-")

    1 2 3
1-2-3

    The newline at the end can be replaced too, with the terminator argument. An empty terminator keeps the next output on the same line:

    print("a", terminator: "")
print("b")

    ab

    Numbers and text are different

    A number is written without quotes. Text, called a string, goes in double quotes. The two can print identically, but they are different things to Swift:

    print(12 + 3)
print("12" + "3")

    15
123

    The first line does arithmetic on numbers. The second joins two strings. Strings get their own lesson; for now, remember that quotes turn a value into text.

    Common mistakes

    • Spelling. The function is print, all lowercase. Print(13) and prnt(13) make the compiler report that it cannot find the name in scope.
    • Missing parentheses. print 13 is not a call. Swift needs the parentheses.
    • Unwanted quotes. print("1998") and print(1998) look the same in the console, but only the second one is a number.
    • Expecting a space after a terminator of "". Nothing is added between the outputs, so include any space you want in the text.

    The exercise

    The task is to print the number 1998. Write print, open a parenthesis, type the number without quotes, and close the parenthesis:

    print(1998)

    Running it shows 1998 on its own line.

    Key takeaways

    • print() writes a value to the console.
    • It ends each call with a newline, so separate calls give separate lines.
    • Several values in one call are separated by a space unless you set separator.
    • Use terminator: "" to stay on the same line.
    • Numbers have no quotes. Text is written inside double quotes.
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