Provides a functional and class based Dart solution for https://www.99-bottles-of-beer.net/

class-99-bottles-of-beer.dart

library ninetyninebottlesofbeer;

class Song {
  // in Dart, underscore denotes private variables.
  // Private variables are scoped to a library, so you can still access privates
  // within a given file/library from other classes/functions.
  // Note the above declared library name to limit the scope..
  int _numBeers;
  // The number of bottles of beers to sing from.
  int bottlesOfBeer;

  // Constructors in Dart can be defined using {} as syntactic sugar, exposing
  // the local variable name as the parameter value, and auto-assignment, or
  // you can us a more classic parameter based setter style declaration.
  // This example uses both.
  Song({this.bottlesOfBeer}) {
    this._numBeers = this.bottlesOfBeer;
  }

  void reset() {
    // In Dart, you don't have to specify `this.` to denote class level
    // variables, but it certainly makes it clearer for developers between
    // local and class level variables if you do.
    _numBeers = bottlesOfBeer;
  }

  // sing uses a number of ternaries combined with string interpolation to print
  // out our wonderful song.
  void sing() {
    String numBeers = this._numBeers.toString();
    int newBeers = --this._numBeers;

    if (this._numBeers == 0) {
      numBeers = 'no more';
      this.reset();
    }

    String oldBottles = numBeers == '1' ? 'bottle' : 'bottles';
    String newBottles = newBeers == 1 ? 'bottle' : 'bottles';
    String lastLine = numBeers != 'no more'
        ? 'take one down, pass it around, $newBeers $newBottles of beer on the wall.'
        : 'Go to the store, buy some more, $newBeers bottles of beer on the wall.';

    print('''
$numBeers $oldBottles of beer on the wall, $numBeers $oldBottles of beer.
$lastLine
  ''');
  }
}

void main() {
  int numberOfBeers = 99;
  Song numberOfBeersOnTheWall = Song(bottlesOfBeer: numberOfBeers);

  // Dart uses C-Style for looping.
  for (int i = numberOfBeers; i >= 1; i--) {
    numberOfBeersOnTheWall.sing();
  }
}

functional-99-bottles-of-beers.dart

// sing uses a number of ternaries combined with string interpolation to print
// out our wonderful song.
void sing(String numBeers, int newBeers) {
  String oldBottles = numBeers == '1' ? 'bottle' : 'bottles';
  String newBottles = newBeers == 1 ? 'bottle' : 'bottles';
  String lastLine = numBeers != 'no more'
      ? 'take one down, pass it around, $newBeers $newBottles of beer on the wall.'
      : 'Go to the store, buy some more, $newBeers bottles of beer on the wall.';

  print('''
$numBeers $oldBottles of beer on the wall, $numBeers $oldBottles of beer.
$lastLine
  ''');
}

// Dart uses void main to define where an app starts executing.
void main() {
  // In Dart, types are declared before the variable name.
  int bottlesOfBeers = 99;

  // Dart uses C-Style for looping.
  for (int numBeers = bottlesOfBeers; numBeers >= 1;) {
    // Dart supports pre-incrementing, for a reminder:
    //   ++i increments i and evaluates to the new value of i.
    //   i++ evaluates to the old value of i, and increments i.
    sing(numBeers.toString(), --numBeers);
  }

  // We've reached our base case!
  sing('no more', bottlesOfBeers);
}

For completeness, there are multiple accepted loop styles in Dart:

void main() {
  // For
  for (int i = 0; i < 10; i++) {
    print(i);
  }

  // For-In
  List<int> indices = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
  for (int index in indices) {
    print(index);
  }

  // While
  int i = 0;
  while (i < 10) {
    print(i);
    i++;
  }

  // Do-While
  i = 0;
  do {
    print(i);
    i++;
  } while (i < 10);
}