Dart Variables

A Dart variable is a piece of memory that can contain a data value. Variables are typically used to store information which your Dart program needs to do its job. These variables are case sensitive.
To declare a variable, write var directly before the variable. The following example gives you an idea about how to use a variable called x :

main() {

  print('Welcome to Android ATC');

  var x=1;

  print(x);

  }

When you run this Dart program, you will get the following result for x value:

You also can declare the variables outside the main() function body as illustrated in the following example:

var y=2;

main() {

  print('Welcome to Android ATC');

  var x=1;

  print(x);

  print(y);

  }

When you run this Dart program, you will get the following result for x and y values:

Dart Data Types

The basic data types used in Dart are strings, Booleans, numbers, lists, and maps.
The following are examples with some details about each data type:
 

1) String

main() {

  String Name= 'William';

  print(Name);

  }

The following is the run result of the above Dart code:

2) Booleans

main() {

  bool xyz;

  xyz = 12 > 5;

  print(xyz);

}

The following is the run result of the above Dart code :

If you changed the formula to xyz=12 < 5; and run the code, the run output will be : false. This is because xyz variable has been declared as a Boolean variable.

3) Numbers

To declare an integer variable, write int directly before the variable.
The following example shows how to declare integer variables and use them in a sum formula:

main() {

  int x=3;

  int y=2;

  int z=x+y;

  print(z);

   }

The following is the run result of the above Dart code:

If you want to use a decimal number, you must use double data type. To declare a double variable, write double directly before the variable as illustrated in the following code:

main() {

double height=1.5;

double width=2.6;

double area=height*width;

print(area);

}

The following is the run result of the above Dart code :

Also, as it illustrated in the following code, you may use "num" to declare an integer or a double number.

main() {

  num x=1;

  num y=1.5;

  num z=x*y;

  print(z);

}

Here, x is declared implicitly as an integer number; however, y is declared implicitly as a double number.
The following is the run result of the previous Dart code:

You can say in a simple way, we will use integer for whole numbers and double for decimal numbers.

4) Lists

A very commonly used collection in programming is an array. Dart represents arrays in the form of List objects. If you want to store a large number of data items for the same variable, you need to use the list. A list is used to store a group of values, all of which have the same data type.

As you see in the following figure, this list contains 10 values starting from list [0] whose value is 14 until list [9] whose value is 45.

Example:
The following code includes a list called test_list contains 10 different values :

main() {

  var test_list = [7,3,100,50,9,30,8,11,6,-4];



  print(test_list[2]);

}

The following is the run result of the previous Dart code :

Also, you can write the same previous list code and declare their data type as integer as follows:

main() {

  List test_list = [7,3,100,50,9,30,8,11,6,-4];



  print(test_list[2]);

}

The run result is the same : 100

Example:
The following code is to print the all the content of the List test_list :

main() {

  var test_list = [7,3,100,50,9,30,8,11,6,-4];



  print(test_list);

}

The following is the run result of the above Dart code :

Example:
In the following Dart code, you will see how to use the add method to add a new value to the existing List. The new value will be added at the end of this List.

main() {

  var test_list = [7,3,100,50,9,30,8,11,6,-4];

  test_list.add(400);

  print(test_list);

}

The following is the run result of the above Dart code :

Example:
In the following Dart code, test_list.length method represents the number of the list length. Here in this example, the list contains 10 numbers from test_list[0] until test_list[9].

main() {

  var test_list = [7,3,100,50,9,30,8,11,6,-4];



  print(test_list.length);

}

The following is the run result of the above Dart code :

Example:
As illustrated in the following Dart code, the for Each method is used to print each list element.

main() {

  var test_list = [7,3,100,50,9,30,8,11,6,-4];

  test_list.forEach((x){

  print(x);

  });

}

5) Maps

Example:

main() {

  var info = {'UserName':'Kevin@androidatc.com','Password':'pass123'};

  print(info);

}

The following is the run result of the above Dart code :

• Declare Maps Using a Map Constructor :
To declare a Map using a Map constructor, there are two steps. First, declare the map as follows:
var info = new Map();

The second, initialize the map as follows:

info['UserName'] = 'kevin@androidatc.com';

Example:

main() {

  var info = new Map();

  info['UserName'] = 'kevin@androidatc.com';

  info['Password'] = 'Canada@123';

  info['Country'] = 'Canada';

  info['City'] = 'Toronto';

  print(info);

}

The following is the run result of the above Dart code :

Explicitly an Implicitly Data type

The following example displays how you can declare a data type both explicitly and
implicitly for variables:

main() {

 var x=10; // implicitly Integer number

 int y=20; // explicitly Integer number

 var city="Toronto"; // implicitly String

 String country="Canada";  // explicitly String

  }

Data type Conversions

In some cases, you may need to convert a data type for a variable to another data type such as changing an Integer to a String. To do that, you need to use toString() function explicitly to convert the variable to data type String, as illustrated in the following figure:

* This topic is a part of lesson 2 of Flutter Application Development course. For more information about this course, click here.