built in data type.dart

The Dart language has special support for the following types:

numbers
strings
booleans
lists (also known as arrays)
sets
maps
runes (for expressing Unicode characters in a string)
symbols

every variable in Dart refers to an object—an instance of a class—you can usually use constructors to initialize variables. 
Some of the built-in types have their own constructors. For example, you can use the Map() constructor to create a map.

Number

int
Integer values no larger than 64 bits.

double
64-bit (double-precision) floating-point numbers.

Both int and double are subtypes of num. The num type includes basic operators such as +, -, /, and *, and is also where you’ll find abs(), ceil(), and floor(), among other methods.

  // String -> int
  var one = int.parse('1');
  assert(one == 1);

// String -> double
  var onePointOne = double.parse('1.1');
  assert(onePointOne == 1.1);

// int -> String
  String oneAsString = 1.toString();
  assert(oneAsString == '1');

// double -> String
  String piAsString = 3.14159.toStringAsFixed(2);
  assert(piAsString == '3.14');
  print(one);