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Hello world

The following code is a basic Dart script, so let's take a look:

main() { // the entrypoint of an Dart app
    var a = 'world'; // declaring and initializing variable
    print('hello $a'); // call function to print to display output
}

This code contains some basic language features that need highlighting:

Every Dart app must have an entry point top-level function (you can refer to Chapter 2, Intermediate Dart Programming, for more information on top-level functions), that is, the main() function.

If you choose to run this code locally on your preconfigured machine with Dart SDK, save the contents to a Dart file, and then run it with a Dart tool in a Terminal, for example, dart hello_world.dart. This will execute the main function of the Dart script.

As we have seen before, although Dart is type-safe, type annotations are optional. Here, we declare a variable with no type and assign a String literal to it.
A String literal can be surrounded with single or double quotes, for example, 'hello world' or "hello world".
To display output on the console, you can use the print() function (which is another top-level function).
With the string interpolation technique, the $a statement inside a String literal resolves the value of the a variable. Dart calls the object's toString() method.

We'll explore more about string interpolation later in this chapter, in the Dart types and variables section, when we talk about the string type.

We can use the //comment syntax to write single-line comments. Dart also has multiline comments with the /* comment */ syntax, as follows:

// this is a single line comment

/*
    This is a long multiline comment
*/

Note the return type of the main function; as it was omitted in the example, it assumes the special dynamic type, which we will explore later.