Contenu du cours

Introduction to Dart

1. First Acquaintance with Dart

Dart Overview Your First Dart Application Function print() in Dart Dart Comments Basic Math Operations

2. Variables and Data Types in Dart

Data Types in Dart Variables in Dart Properties of Numbers in Dart String in Dart Bool, Equality and Relational Operators in Dart

3. Conditional Statements

if Statement in Dart if...else Statement in Dart else-if Statement in Dart switch-sase Statement in Dart

4. List and String

List in Dart Indexes in Dart What are Methods in Dart?String Properties and Methods in Dart

5. Loops in Dart

Introduction to Loops While-Loop in Dart Do-While Loop in Dart For-Loop in Dart Increment and Decrement Break and Continue

Variables in Dart

What is a Variable?

A variable is a named space in the memory that stores values. In other words, it acts a container for values in a program.

A variable must be declared before it is used. Dart uses the var keyword to achieve this. The syntax for declaring a variable is given below.

main


              123
            
void main() {
  var name = 'Alex'; // Variable with String value
}

Code Syntax

A variable in Dart consists of three components: type (e.g., var), name (e.g., name), and value (e.g., "Alex"). The type defines the data type, the name is the identifier used to reference the variable, and the value is the actual data stored in the variable.

Variable Declaration Rules

Variables name must be unique within a block of code;
Variables name can't be the keyword (like var or void);
Variables name should not start with a number;
Variables name must not contain spaces or special symbols, except the underscore(_) and the dollar($) sign.

Example Use Variable

This, we work with the value stored inside the variable:

main


              1234
            
void main() {
  var name = "Bob";  
  print(name);
}

We can write the numbers calculation result or join strings into a variable:

main


              1234
            
void main() {
  var age = 27 + 3;  
  print(age);
}

Keyword Var

When declaring a variable using var, we do not explicitly indicate the type of data that will be stored in this variable. Dart automatically determines what data type a variable will contain when it is initialized.

main


              123
            
void main() {
  var age = 27;
}

With such initialization, the age variable will store integer values.

Please note that after initializing a variable with one data type, you cannot reassign the data type for the variable!

main


              1234
            
void main() {
  var age = 10;
  age = "ten"; // Error
}

We have successfully written the value 28 to the variable age but cannot write the String value 28 to this variable.

Type-Checking in Dart

Type-checking in Dart is the process of verifying that the data types used in the code match the expected data types. It helps prevent errors such as assigning a value of the wrong type to a variable.

Type Annotations

To improve the readability and structure of the code, you need to use type annotations. To do this, instead of the var keyword, we write the variable's data type.

Syntax comparison of type annotation and keyword var:

Type annotations are optional in Dart since the Dart can usually determine the type of a variable by its initial value. However, using type annotations is recommended as it can help prevent errors and make your code more readable and understandable.

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Section 2. Chapitre 2

Introduction to Dart

Variables in Dart

What is a Variable?

Code Syntax

Variable Declaration Rules

Example Use Variable

Keyword Var

Type-Checking in Dart

Type Annotations

Define a variable.