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 :

1. Numbers
2. Strings
3. Booleans
4. Lists
5. Maps
6. Sets
7. Runes
8. 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:

Numbers

When you need to store numeric value on dart, you can use either int or double. Both int and double are subtypes 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");  
   
}

Num 1 is 100
Num 2 is 130.2
Num 3 is 50
Num 4 is 50.4
Sum is 330.59999999999997

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 numbers like 2, 3, 4, etc.

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

1130.22

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");   
}

School name is Diamond School and address is New York 2140

Create A Multi-Line String In Dart

If you want to create a multi-line String in dart, then you can use triple quotes 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");
}

Multiline text is This is Multi Line Text
with 3 single quote
I am also writing here.

Other multiline text is This is Multi Line Text
with 3 double quote
I am also writing here.

Special Character In String

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

I am from 
US.
I am from 	US.

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 price value
num price = 10;
String withoutRawString = "The value of price is \t $price"; // regular String
String withRawString =r"The value of price is \t $price"; // raw String

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

}

Without Raw: The value of price is 	 10
With Raw: The value of price is \t $price

Type Conversion In Dart

In dart, type conversion allows you to convert one data type to another 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}");
}

Type of strvalue is String
Value of intvalue is 1
Type of intvalue is int

Convert String To Double In Dart

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

void main() {
String strvalue = "1.1";
print("Type of strvalue is ${strvalue.runtimeType}");
double doublevalue = double.parse(strvalue);
print("Value of doublevalue is $doublevalue");
// this will print data type
print("Type of doublevalue is ${doublevalue.runtimeType}");
}

Type of strvalue is String
Value of doublevalue is 1.1
Type of doublevalue is double

Convert Int To String In Dart

You can convert int to String using the 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}");
}

Type of one is int
Value of oneInString is 1
Type of oneInString is String

Convert Double To Int In Dart

You can convert double to int using the 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}");
}

The value of num1 is 10.01. Its type is double
The value of num2 is 10. Its type is int

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");
}

Married Status: true

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");
}

Value of names is [Raj, John, Max]
Value of names[0] is Raj
Value of names[1] is John
Value of names[2] is Max
The Length of names is 3

Sets

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

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

{Sun, Mon, Tue, Wed, Thu, Fri, Sat}

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'
};
// displaying the output
print(myDetails['name']);
}

John Doe

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);
}

John Doe
20

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);
}

(97)

How To Check Runtime Type

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

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

int
true

Optionally Typed Language

You may have 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);
}

Error:
A value of type 'String' can't be assigned to a variable of type 'int'.

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);
}

Hello

Video

Watch our video on Dart datatypes.