Explain the syntax and usage of variables in Dart.

In Dart, variables are used to store and manipulate data within a program. They are fundamental components of any programming language and play a crucial role in storing values that can be accessed and modified throughout the execution of the program. Understanding the syntax and usage of variables in Dart is essential for effectively working with data and performing operations.

Syntax:
In Dart, variables are declared using the `var` keyword followed by the variable name, an optional type annotation, and an optional initial value. The general syntax for variable declaration in Dart is as follows:

```
dart`var variableName;`
```
or

```
dart`type variableName;`
```
or

```
dart`type variableName = initialValue;`
```
Usage:

1. Variable Declaration and Initialization:
You can declare a variable without specifying its type explicitly by using the `var` keyword. Dart's type inference mechanism automatically determines the type based on the assigned initial value. For example:

```
dart`var name = 'John';
var age = 25;
var isStudent = true;`
```
Alternatively, you can declare a variable with an explicit type annotation, specifying the data type of the variable. For example:

```
dart`String name = 'John';
int age = 25;
bool isStudent = true;`
```
It's also possible to declare a variable and assign an initial value at the same time. For example:

```
dart`String name = 'John';`
```
2. Variable Assignment and Reassignment:
Once a variable is declared, its value can be assigned or reassigned using the assignment operator (`=`). For example:

```
dart`var count = 10;
count = 20; // Reassigning the value of 'count' variable`
```
It's important to note that variables in Dart are mutable by default, meaning their values can be changed throughout the execution of the program.
3. Variable Types:
Dart supports various built-in data types for variables, including:

* Numbers: `int` (integers) and `double` (floating-point numbers)
* Strings: `String` (sequence of characters)
* Booleans: `bool` (true or false)
* Lists: `List` (ordered collection of objects)
* Maps: `Map` (collection of key-value pairs)Dart also allows the declaration of custom data types using classes or typedefs.
4. Variable Scope:
Variables in Dart have a specific scope within which they are accessible. The scope is defined by the block in which the variable is declared. Variables declared inside a block are only accessible within that block or its nested blocks.
5. Variable Naming Conventions:
Dart follows camelCase naming conventions for variables. Variable names should be descriptive and meaningful, starting with a lowercase letter. For example:

```
dart`var studentName = 'John Doe';
var numberOfCourses = 5;`
```
It's important to choose appropriate variable names to enhance code readability and maintainability.

Overall, understanding the syntax and usage of variables in Dart is essential for effectively working with data and manipulating values within a program. By declaring variables, assigning values, and utilizing appropriate types, you can store and manipulate data effectively to create robust and dynamic applications.