Data types in flutter or dart

Overview

Dart is a statically typed language, meaning every variable has a type. Flutter/Dart supports a rich set of built-in data types.

Core Data Types

Numbers

dartCopy
int age = 25;           // Whole numbers (64-bit signed)
double price = 9.99;    // Decimal numbers (64-bit floating point)
num mixed = 3;          // Either int or double
mixed = 3.14;           // ✅ num can hold both

// Int operations
print(10 ~/ 3);   // 3 (integer division)
print(10 % 3);    // 1 (modulo)
print(2.pow(8));  // Use dart:math: pow(2, 8) = 256

String

dartCopy
String name = 'Alice';
String greeting = "Hello, $name!"; // Interpolation
String multiLine = '''
  This is a
  multi-line string
''';

// Common operations
print(name.length);          // 5
print(name.toUpperCase());   // ALICE
print(name.contains('Ali')); // true
print(name.substring(0, 3)); // Ali
print(name.split(''));        // [A, l, i, c, e]

Boolean

dartCopy
bool isActive = true;
bool isLoggedIn = false;

// Dart requires explicit booleans (no truthy/falsy like JS)
if (isActive) print('Active');    // ✅
// if (1) print('truthy');        // ❌ Error in Dart

List (Array)

dartCopy
List<int> numbers = [1, 2, 3, 4, 5];
var fruits = ['apple', 'banana', 'cherry']; // Type inferred

numbers.add(6);
numbers.removeAt(0);
print(numbers.length);
print(numbers[0]);
numbers.sort();

Map (Dictionary/HashMap)

dartCopy
Map<String, int> scores = {'Alice': 95, 'Bob': 87};
var config = {'theme': 'dark', 'fontSize': 14};

scores['Charlie'] = 91;
print(scores['Alice']);           // 95
print(scores.containsKey('Bob')); // true

Set

dartCopy
Set<String> tags = {'flutter', 'dart', 'mobile'};
tags.add('dart');         // Duplicate — ignored
print(tags.length);       // 3
print(tags.contains('flutter')); // true

Null

dartCopy
int? nullableAge = null; // Nullable with ?
String? name = null;

// Null-safe access
print(name?.length);     // null (no crash)
print(name ?? 'Guest');  // Guest (default if null)

Dynamic & Object

dartCopy
dynamic anything = 42;
anything = 'now a string'; // No type error

Object obj = 42;
obj = 'string'; // ✅ Object? can be null too

Type Summary

int

42

double

3.14

num

3

3.14

String

'hello'

bool

true/false

List<T>

[1, 2, 3]

Map<K,V>

{'a': 1}

Set<T>

{1, 2, 3}

dynamic

Null

null