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Learn Dart: First Step to Flutter

Understanding the Code

Let’s go over each line of a basic Hello World program in Dart.

We'll cover the following...

Overview

Just to refresh our minds, let’s take a look at the code for our Hello World application.

Dart
main() {
  // Printing the text 'Hello World'
  print("Hello World");
}

The Print Statement

On line 3 of the program, we are using a print statement which prints the text Hello World. print() is used to display the output of the code on the console. It follows this syntax:

print( Insert what you want to print here )

Since Hello World is text, to be able to print it, we need to enclose it in quotation marks. The syntax for displaying text is as follows:

print( "Insert text to be printed" )

Nothing without a semicolon

You might have noticed that the print statement on line 3 ends with a semicolon.

print("Hello World");

In Dart, just as in most programming languages, each statement needs to end with a semi-colon for the program to execute successfully. Try removing the semi-colon in the code snippet above and see what happens.

Comments

Line 2 of the program is a comment. Comments come in handy for developers that want to read or study code someone else has written. They enable you to write descriptions about the code without it affecting the program in any way whatsoever. Our comment is to let the reader know that the program is printing the text Hello World. The general syntax is as follows:

// Insert comment here

You simply need to type two forward slashes followed by the description you want to write.

Imperative programming

The code that appears inside of the main() function gets executed in order of appearance. Let’s modify the code in the snippet above and try printing From Dart along with Hello World.

Dart
main() {
  print("Hello World");
  print("From Dart");
}

When you run the code above, the print statement on line 2 will execute first and then the second print statement on line 3 will execute.

This style of programming is called imperative programming. It is essentially a programming paradigm wherein you write a set of instructions that execute in sequential order. Imperative programming doesn’t necessarily describe what the program should accomplish, rather it shows how the program should accomplish it. So, in this case, we have created a program that goes first and prints out the text Hello World and then moves on to the next line and prints the text From Dart.

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