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Day 2 (Flutter Excelr)

  1. Data Types
  2. Collections / Iterables
  3. Type Casting in Dart
  4. Operators
  5. Control flow in Dart
  6. Functions in Dart

Data Types

Always prefer var to declare variables

Built-in types

  1. Numbers --> num (int, double)

        var x = 5;
    var y = 3.6;

    //num variables can hold both int and double values
    num x = 1;
    num y = 5.6;

    int a = 1.2; // error
    double b = 5;

  2. Booleans --> bool (true, false)

  3. Strings --> String

        String singleQuote = 'allowed';
    String doubleQuote = "also allowed";
    String multiLine = '''
        This is
        multi line
        string in dart''';
    String rawString = r"It is raw string \n will not work here";

Collections / Iterables

  1. Lists --> (List, array in other languages)

    A List is an ordered group of items.

        var list = [1, 2, 3, 'Boat',];
    var constantList = const [1, 2, 3];
    var emptyList = [];

    // copy one list to another using spread operator [...]
    var list2 = [...list];

  2. Sets --> (Set)

    A Set is an unordered group of unique items

        var primeSet = {1, 3, 17};
    var emptySet = {}; // Creates an empty map, not a set
    var emptySet = <String>{};

    // copy one set to another using spread operator {...}
    var set2 = {2, ...primeSet};

  3. Maps --> (Map)

    A Map is an unordered collection of key:value pairs, similar to a dictionary in Python

        var map = {
        1: 'dart',
        2: 'flutter',
    };

    var emptyMap = {};

    // copy one map to another using spread operator {...}
    var map2 = {0: 'english', ...map};

Control-flow operators(if and for) with Collections

    var list = [1, 2, 3, 4, 5];

    // Using if in a collection
    var evenList = [for (var i in list) if (i % 2 == 0) i];
    print(evenList); // prints: [2, 4]

    // Using for in a collection
    var incrementedList = [for (var i in list) i + 1];
    print(incrementedList); // prints: [2, 3, 4, 5, 6]

Type Casting in Dart

    // implicit type casting or type inference (auromatically detect type of variable)
    var num = 5;

    // String -> int
    var one = int.parse('1'); // explicit type casting
    print(one); // 1

    // String -> double
    var onePointOne = double.parse('1.1'); // explicit type casting
    print(onePointOne); // 1.1

    // int -> String
    String oneAsString = 1.toString(); // explicit type casting
    print(oneAsString); // '1'

    // double -> int
    double myDouble = 123.45;
    int myInt = myDouble.toInt();
    print(myInt); // 123

Operators

  1. Arithmetic Operators (+, -, *, /, %, ~/, -const)

    • [~/ in dart ➡ // in Python]

  2. Relational Operators (<, >, <=, ==, !=, etc)

  3. Type Test Operators (is, is !)

    String name = 'Ram';

print(name is String); // prints true

  4. Bitwise Operators (&, |, ~, ^, <<, >>)

  5. Assignment Operators (=, ??=)

        // ??= [Assign value to x if it is null; otherwise, x stays the same]

    var x;
    x ??= 5; // Value is assigned as x is null
    x ??= 10; // Value is not assigned as x is not null

  6. Logical Operators (&&, ||, !)

    • Logical operators are only applicable to boolean expressions
    • non-zero numbers are not considered as true and zero not as false
    • 0 and 1 are not boolean instead int

  7. Conditional Operators / Ternary operators (?: and ??)

    • (condition ? expr1 : expr2)

      If condition is true, evaluates expr1 (and returns its value); otherwise, evaluates and returns the value of expr2

    • (expr1 ?? expr2)

      If expr1 is null, returns expr2; otherwise, evaluates and returns the value of expr1

        int a = 5, b = 8;
    a > b ? print(a) : print(b);

    String? name; // made name nullable using ?
    String nameToUse = name ?? 'Guest'; // Null coalescing operator

  8. Cascade Notation Operator (..)

    used to perform multiple method calls or multiple operations on same object

    class MyClass {
    void methodA() {
        print('Method A');
    }

    void methodB() {
        print('Method B');
    }
}

void main() {
    MyClass myObject = MyClass();

    // without using cascade notation
    myObject.methodA();
    myObject.methodB();

    // Using cascade notation
    myObject
     ..methodA()
     ..methodB();
}

// output
    Method A
    Method B

Control flow in Dart

  • if-else

  • switch-case

    var animal = 'Dog';

switch (animal) {
    case 'Dog':
        print('You have a dog.');
        break;
    case 'Bird':
        print('You have a bird.');
        break;
    default:
        print('Animal not recognized.');
}

  • for loop (for, for-in, for-each)

    // for loop
for (var i = 0; i < 5; i++) {
    print(i); // 0 1 2 3 4
}

// for-in loop
var word = ['f', 'o', 'r', 'i', 'n'];

for (var letters in word) {
    print(letters); // f o r i n
}

// for-each loop
word.forEach(print); // f o r i n

  • while loop when we don't know the number of iterations

  • do-while loop executes once then checks the condition

  • break and continue

Functions in Dart

  • code reusability

  • return type is optional, dynamic if not specified

  • datatype of parameters is optional, dynamic if not specified

  • arguments: visible in fn call (actual parameters)

  • parameters: visible in fn definition (formal parameters)

  • Parameter types:

    • positional: (int x, int y)

      called like fn(5, 6)

    • named: ({int x, int y}) , { } indicates named parameters

      called like fn(x: 5, y: 6)

    • default: (x, [y = 0]), [ ] indicates default parameters

      called like fn(5)

    • optional:
      • positional: ([int? x, int? y])

        called like fn(5, 6)

      • named: ({x, int? y})

        called like fn(x: 5, y: 6)

      • default: (int? x, [y = 10])

        called like fn(5)

  • Anonymous fn / Lambda fn / fat arrow / single line fn

        var sum = (int x, int y) => x + y;
    print(sum(5, 6)); // 11

  • Function as first-class objects

    as they can be assigned to variables or passed as arguments to other functions

        void main() {
        var sum = (int x, int y) => x + y;
        print(sum(5, 6)); // 11

        var myFn = sum;
        print(myFn(5, 6)); // 11
    }

Day 3 notes