Data Types in Dart

Data Types

Data types help you to categorize all the different types of data you use in your code. For e.g. numbers, texts, symbols, etc. The data type specifies what type of value will be stored by the variable. Each variable has its data type. Dart supports the following built-in data types :

Numbers
Strings
Booleans
Lists
Maps
Sets
Runes
Null

Built-In Types

In Dart language, there is the type of values that can be represented and manipulated. The data type classification is as given below:

Data Type	Keyword	Description
Numbers	int, double, num	It represents numeric values
Strings	String	It represents a sequence of characters
Booleans	bool	It represents Boolean values true and false
Lists	List	It is an ordered group of items
Maps	Map	It represents a set of values as key-value pairs
Sets	Set	It is an unordered list of unique values of same types
Runes	runes	It represents Unicode values of String
Null	null	It represents null value

Numbers

When you need to store numeric value on dart, you can use either int or double. Both int and double are subtype of num. You can use num to store both int or double value.

 void main() {
 // Declaring Variables  
int num1 = 100; // without decimal point.
double num2 = 130.2; // with decimal point.
num num3 = 50;
num  num4 = 50.4;  

// For Sum   
num sum = num1 + num2 + num3 + num4;
   
// Printing Info   
print("Num 1 is $num1");
print("Num 2 is $num2");  
print("Num 3 is $num3");  
print("Num 4 is $num4");  
print("Sum is $sum");  
   
}

Round Double Value To 2 Decimal Places

The .toStringAsFixed(2) is used to round the double value upto 2 decimal places in dart. You can round to any decimal places by entering number like 2, 3, 4.

void main() {
// Declaring Variables
double prize = 1130.2232323233233; // valid.
print(prize.toStringAsFixed(2));
}

String

String helps you to store text data. You can store values like I love dart, New York 2140 in String. You can use single or double quotes to store string in dart.

void main() {
// Declaring Values     
String schoolName = "Diamond School";
String address = "New York 2140";   

// Printing Values
print("School name is $schoolName and address is $address");   
}

Create A Multi-Line String In Dart

If you want to create a multi-line String in dart, then you can use triple quote with either single or double quotation marks.

 void main() {
// Multi Line Using Single Quotes   
String multiLineText = '''
This is Multi Line Text
with 3 single quote
I am also writing here.
''';
   
// Multi Line Using Double Quotes   
String otherMultiLineText = """
This is Multi Line Text
with 3 double quote
I am also writing here.
""";
   
// Printing Information   
print("Multiline text is $multiLineText");
print("Other multiline text is $otherMultiLineText");
}

Special Character In String

Special Character	Work
\n	New Line
\t	Tab

 void main() {
   
// Using \n and \t   
print("I am from \nUS.");
print("I am from \tUS.");
}

Create A Raw String In Dart

You can also create raw string in dart. Special characters won’t work here. You must write r after equal sign.

 void main() {
// Set prize value
num prize = 10;
String withoutRawString = "The value of prize is \t $prize"; // regular String
String withRawString =r"The value of prize is \t $prize"; // raw String

print("Without Raw: $withoutRawString"); // regular result
print("With Raw: $withRawString"); // with raw result

}

Type Conversion In Dart

In dart, type conversion allows you to convert one data type to other type. For e.g. to convert String to int, int to String or String to bool, etc.

Convert String To Int In dart

You can convert String to int using int.parse() method. The method takes String as an argument and converts it into an integer.

void main() {
String strvalue = "1";
print("Type of strvalue is ${strvalue.runtimeType}");   
int intvalue = int.parse(strvalue);
print("Value of intvalue is $intvalue");
// this will print data type
print("Type of intvalue is ${intvalue.runtimeType}");
}

Convert Int To String In Dart

You can convert int to String using toString() method. Here is example:

void main() {
int one = 1;
print("Type of one is ${one.runtimeType}");
String oneInString = one.toString(); 
print("Value of oneInString is $oneInString");
// this will print data type
print("Type of oneInString is ${oneInString.runtimeType}");
}

Convert Double To Int In Dart

You can convert double to int using toInt() method.

void main() { 
   double num1 = 10.01;
   int num2 = num1.toInt(); // converting double to int

  print("The value of num1 is $num1. Its type is ${num1.runtimeType}");
  print("The value of num2 is $num2. Its type is ${num2.runtimeType}");
}

Booleans

In Dart, boolean holds either true or false value. You can write the bool keyword to define the boolean data type. You can use boolean if the answer is true or false. Consider the answer to the following questions:

Are you married?
Is the door open?
Does a cat fly?
Is the traffic light green?
Are you older than your father?

These all are yes/no questions. Its a good idea to store them in boolean.

void main() {
bool isMarried = true;
print("Married Status: $isMarried");
}

Lists

The list holds multiple values in a single variable. It is also called arrays. If you want to store multiple values without creating multiple variables, you can use a list.

void main() {
List<String> names = ["Raj", "John", "Max"];
print("Value of names is $names");
print("Value of names[0] is ${names[0]}"); // index 0
print("Value of names[1] is ${names[1]}"); // index 1
print("Value of names[2] is ${names[2]}"); // index 2

  // Finding Length of List 
int length = names.length;  
print("The Length of names is $length");
}

Info

Note: List index always starts with 0. Here names[0] is Raj, names[1] is John and names[2] is Max.

Sets

An unordered collection of unique items is called set in dart. You can store unique data in sets.

Info

Note: Set doesn’t print duplicate items.

void main() {
Set<String> weekday = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
print(weekday);
}

Maps

In dart, a map is an object where you can store data in key-value pairs. Each key occurs only once, but you can use same value multiple times.

void main() {
Map<String, String> myDetails = {
   'name': 'John Doe',
   'address': 'USA',
   'fathername': 'Soe Doe'
};

print(myDetails['name']);
}

Var Keyword In Dart

In dart, var automatically finds a data type. In simple terms, var says if you don’t want to specify a data type, I will find a data type for you.

void main(){
var name = "John Doe"; // String
var age = 20; // int

print(name);
print(age);
}

Runes In Dart

With runes, you can find Unicode values of String. The Unicode value of a is 97, so runes give 97 as output.

void main() {

String value = "a";
print(value.runes);
}

How To Check Runtime Type

You can check runtime type in dart with .runtimeType after variable name.

void main() { 
   var a = 10;
   print(a.runtimeType); 
   print(a is int); // true
}

Optionally Typed Language

You may heard of the statically-typed language. It means the data type of variables is known at compile time. Similarly, dynamically-typed language means data types of variables are known at run time. Dart supports dynamic and static types, so it is called optionally-typed language.

Statically Typed

A language is statically typed if the data type of variables is known at compile time. Its main advantage is that the compiler can quickly check the issues and detect bugs.

void main() { 
   var myVariable = 50; // You can also use int instead of var
   myVariable = "Hello"; // this will give error
   print(myVariable);
}

Dynamically Typed Example

A language is dynamically typed if the data type of variables is known at run time.

void main() { 
   dynamic myVariable = 50;
   myVariable = "Hello";
   print(myVariable);
}

Info

Note: Using static type helps you to prevent writing silly mistakes in code. It’s a good habit to use static type in dart.

Video

Watch our video on Dart datatypes.