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Print a literal string on standard output
print("Hello World");
Loop to execute some code a constant number of times
print("Hello\n" * 10);
Alternative implementation:
for (var i = 0; i < 10; i++)
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)
void finish(String name) {
  print("My job here is done. Goodbye $name.");
Create a function which returns the square of an integer
int square(int x) => x * x;
Declare a container type for two floating-point numbers x and y
class Point {
  double x, y;
Alternative implementation:
class Point {
  double x, y;
  Point(this.x, this.y);
Do something with each item x of the list (or array) items, regardless indexes.
Print each index i with its value x from an array-like collection items
for (var i = 0; i < items.length; i++) {
  print('index=$i, value=${items[i]}');
Alternative implementation:
items.asMap().forEach((i, x) {
  print('index=$i, value=$x');
Alternative implementation:
items.forEachIndexed((i, x) {
  print('index=$i, value=$x');
Create a new map object x, and provide some (key, value) pairs as initial content.
var x = {
	"one": 1,
	"two": 2
The structure must be recursive because left child and right child are binary trees too. A node has access to children nodes, but not to its parent.
class Node<T> {
  final T value;
  Node<T> left, right;
  Node(this.value, {this.left, this.right});
Generate a random permutation of the elements of list x
Alternative implementation:
var shuffled = x.toList()..shuffle();
The list x must be non-empty.
x[new Random().nextInt(x.length)];
Check if the list contains the value x.
list is an iterable finite container.
Access each key k with its value x from an associative array mymap, and print them.
mymap.forEach((k, v) => print('Key=$k, Value=$v'));
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.
double pick(num a, num b) => a + new Random().nextDouble() * (b - a);
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b.
int pick(int a, int b) => a + Random().nextInt(b - a + 1);
Call a function f on every node of binary tree bt, in depth-first infix order
traverse(Node bt, f(value)) {
   if (bt == null) return;
   traverse(bt.left, f);
   traverse(bt.right, f);
The structure must be recursive. A node may have zero or more children. A node has access to its children nodes, but not to its parent.
class Node<T> {
  final T value;
  final List<Node<T>> children;
  Node(this.value, this.children);
Call a function f on every node of a tree, in depth-first prefix order
traverse(Tree node, f(value)) {
  for (var child in node.children) { 
    traverse(child, f);
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering.
x = x.reversed.toList();
Implement a function search which looks for item x in a 2D matrix m.
Return indices i, j of the matching cell.
Think of the most idiomatic way in the language to return the two values at the same time.
class Position {
  int i, j;
  Position(this.i, this.j);
Position search(List<List> m, x) {
  for (var i = 0; i < m.length; i++) {
    var line = m[i];
    for (var j = 0; j < line.length; j++) {
      if (line[j] == x) {
        return new Position(i, j);
  return null;
Swap the values of the variables a and b
var tmp = a;
a = b;
b = tmp;
Extract the integer value i from its string representation s (in radix 10)
var i = int.parse(s);
Given a real number x, create its string representation s with 2 decimal digits following the dot.
var s = x.toStringAsFixed(2);
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese)
var s = "ネコ";
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
Declare and initialize a matrix x having m rows and n columns, containing real numbers.
var x = new List.generate(m, (_) => new List(n));
Alternative implementation:
var x = new List.generate(m, (_) => new List.filled(n, 0));
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
var x = new List.generate(m, (_) => 
                new List.generate(n, (_) => 
                    new List.filled(p, 0.0), 
                    growable: false), 
                growable: false);
Sort the elements of the list (or array-like collection) items in ascending order of x.p, where p is a field of the type Item of the objects in items.
items.sort((a, b) =>, b.p));
Alternative implementation:
items.sort((a, b) => (a.p).compareTo(b.p));
Remove i-th item from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
Note that in most languages, the smallest valid value for i is 0.
Launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
for (int i = 1; i <= 1000; i++) {
Create the recursive function f which returns the factorial of the non-negative integer i, calculated from f(i-1)
f(i) => (i == 0) ? 1 : i * f(i - 1);
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers.
int exp(int x, int n) {
  if (n == 0) return 1;
  if (n == 1) return x;
  var r = exp(x * x, n ~/ 2);
  if (n % 2 == 1) r *= x;
  return r;
Alternative implementation:
int exp(int x, int n) {
  var r = 1;
  while (true) {
    if (n.isOdd) r *= x;
    n ~/= 2;
    if (n == 0) break;
    x *= x;
  return r;
Assign to the variable x the new value f(x), making sure that no other thread may modify x between the read and the write.
x = f(x);
Declare and initialize a set x containing unique objects of type T.
var x = new Set<T>();
Implement a function compose (A -> C) with parameters f (A -> B) and g (B -> C), which returns the composition function g ∘ f
typedef R Func<T,R>(T arg);

Func<A,C> compose(B f(A x), C g(B x)) => (A x) => g(f(x))
Implement a function compose which returns composition function g ∘ f for any functions f and g having exactly 1 parameter.
compose(f, g) => (x) => g(f(x));
Transform a function that takes multiple arguments into a function for which some of the arguments are preset.
curry(f(a, b), a) => (b) => f(a, b);
Find substring t consisting in characters i (included) to j (excluded) of string s.
Character indices start at 0 unless specified otherwise.
Make sure that multibyte characters are properly handled.
var t = s.substring(i, j);
Set the boolean ok to true if the string word is contained in string s as a substring, or to false otherwise.
var ok = s.contains(word);
Create string t containing the same characters as string s, in reverse order.
Original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory.
var t = new String.fromCharCodes(s.runes.toList().reversed);
Alternative implementation:
var t = s.split('').reversed.join();

Print each item v of list a which is not contained in list b.
For this, write an outer loop to iterate on a and an inner loop to iterate on b.
main()  {
  var a = [1, 2, 3];
  var b = [2, 3];

  outer: for (var v in a) {
    for (var w in b) {
      if (w == v) continue outer;
Look for a negative value v in 2D integer matrix m. Print it and stop searching.
OUTER: for (var i = 0; i < m.length; i++) {
  for (var j = 0; j < m[i].length; j++) {
    if (m[i][j] < 0) {
      print("Negative value found at $i,$j: ${m[i][j]}");
      break OUTER;
Insert the element x at position i in the list s. Further elements must be shifted to the right.
s.insert(i, x);
Sleep for 5 seconds in current thread, before proceeding with the next instructions.
sleep(const Duration(seconds: 5));
Alternative implementation:
await new Future.delayed(const Duration(seconds : 5));
Create the string t consisting of the 5 first characters of the string s.
Make sure that multibyte characters are properly handled.
var t = s.substring(0, 5);
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled.
var n = s.length;
var t = s.substring(n-5, n);
Assign to variable s a string literal consisting in several lines of text, including newlines.
var s = '''A
Alternative implementation:
var s = """A
Build list chunks consisting in substrings of the string s, separated by one or more space characters.
s.split(new RegExp('\\s+'))
Write a loop that has no end clause.
while (true) {
  // do something
Alternative implementation:
for (;;) {

Determine whether the map m contains an entry for the key k
Determine whether the map m contains an entry with the value v, for some key.
Concatenate elements of string list x joined by the separator ", " to create a single string y.
y = x.join(', ');
Calculate the sum s of the integer list or array x.
var s = x.fold(0, (a, b) => a + b);
Create the string representation s (in radix 10) of the integer value i.
var s = "$i";
Fork-join : launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
Wait for the completion of the 1000 tasks and then print "Finished".
List<Future> tasks = [];
for (int i = 1; i <= 1000; i++) {
  tasks.add(Isolate.spawn(f, i));
await Future.wait(tasks);
Create the list y containing the items from the list x that satisfy the predicate p. Respect the original ordering. Don't modify x in-place.
var y = x.where(p).toList();
Create the string lines from the content of the file with filename f.
var lines = new File(f).readAsStringSync();
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").
stderr.write("$x is negative");
Assign to x the string value of the first command line parameter, after the program name.
main(args) {
  var x = args[0];
Assign to the variable d the current date/time value, in the most standard type.
var d =;
Set i to the first position of string y inside string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.
var i = x.indexOf(y);
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping.
var x2 = x.replaceAll(y, z);
Assign to x the value 3^247
var x = pow(3, 247);
From the real value x in [0,1], create its percentage string representation s with one digit after decimal point. E.g. 0.15625 -> "15.6%"
var s = "${(x * 100).toStringAsFixed(1)}%";
Calculate the result z of x power n, where x is a big integer and n is a positive integer.
var z = pow(x, n);
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
int binom(int n, int k) {
  int result = 1;
  for (int i = 0; i < k; i++) {
    result = result * (n - i) ~/ (i + 1);
  return result;
Create an object x to store n bits (n being potentially large).
final x = FixedBitArray(n);
Use seed s to initialize a random generator.

If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
var r = new Random(s);
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
var r = new Random(new;
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout.
main(List<String> args) {
  print(args.join(' '));
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
int gcd(int a, int b) {
  while (b != 0) {
    var t = b;
    b = a % t;
    a = t;
  return a;
Alternative implementation:
x = a.gcd(b);
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers.
x = lcm(a, b);

int lcm(int a, int b) => (a * b) ~/ gcd(a, b);

int gcd(int a, int b) {
  while (b != 0) {
    var t = b;
    b = a % t;
    a = t;
  return a;
Alternative implementation:
x = a.lcm(b);

extension LCM on int {
  int lcm(int other) => (this * other) ~/ this.gcd(other);
Create the string s of integer x written in base 2.

E.g. 13 -> "1101"
var s = x.toRadixString(2);
Execute a block once, then execute it again as long as boolean condition c is true.
do {
} while(c);
Declare the floating point number y and initialize it with the value of the integer x .
double y = x.toDouble();
Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x .
Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).
int y = x.toInt()
Declare the integer y and initialize it with the rounded value of the floating point number x .
Ties (when the fractional part of x is exactly .5) must be rounded up (to positive infinity).
var y = x.round();
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2
var c = i.toRadixString(2).replaceAll('0','').length;
Exit immediately.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it.
Create a new bytes buffer buf of size 1,000,000.
var buf = BytesBuilder().addByte(1000000);
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo.
class Foo{
  int _x = 0;
  int get x => _x;  
Read from the file data.json and write its content into the object x.
Assume the JSON data is suitable for the type of x.
Map x = json.jsonDecode(await new File('data.json').readAsString());
Alternative implementation:
Map x = json.jsonDecode(new File('data.json').readAsStringSync());
Write the contents of the object x into the file data.json.
class JsonModel {
  // Create Field
  int id;
  String qrText, licen, trans, name;

//   // Constructor
//   JsonModel(
//       int idInt, String nameString, String userString, String passwordString) {
// //     id=idInt;
// // name =nameString;
// // user =userString;
// // password = passwordString;
//   }

  JsonModel(,, this.licen, this.trans, this.qrText);

  JsonModel.fromJson(Map<String, dynamic> parseJSON) {
    id = int.parse(parseJSON['id']);
    licen = parseJSON['Li
Implement the procedure control which receives one parameter f, and runs f.
control(Function f) => f();
Print the name of the type of x. Explain if it is a static type or dynamic type.

This may not make sense in all languages.
Assign to variable x the length (number of bytes) of the local file at path.
final x = (await File(path).readAsBytes()).length;
Alternative implementation:
var x = File(path).lengthSync();
Set the boolean b to true if string s starts with prefix prefix, false otherwise.
var b = s.startsWith(prefix);
Set boolean b to true if string s ends with string suffix, false otherwise.
var b = s.endsWith(suffix);
Convert a timestamp ts (number of seconds in epoch-time) to a date with time d. E.g. 0 -> 1970-01-01 00:00:00
var d = new DateTime.fromMillisecondsSinceEpoch(ts, isUtc: true);
Assign to the string x the value of the fields (year, month, day) of the date d, in format YYYY-MM-DD.
x = DateFormat('YYYY-MM-DD').format(d);
Sort elements of array-like collection items, using a comparator c.
Assign to the string s the name of the currently executing program (but not its full path).
var s = File(Platform.resolvedExecutable).uri.pathSegments.last;
Set the boolean blank to true if the string s is empty, or null, or contains only whitespace ; false otherwise.
final blank = s == null || s.trim() == '';
Alternative implementation:
bool blank = s?.trim()?.isEmpty ?? true;
Print each key k with its value x from an associative array mymap, in ascending order of k.
var sortedKeys = myMap.keys.toList()..sort();
for (var k in sortedKeys) {
  print("Key=$k Value=${myMap[k]}");
Print each key k with its value x from an associative array mymap, in ascending order of x.
Multiple entries may exist for the same value x.
    ..sort((a, b) => a.value.compareTo(b.value))
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise.
bool b = d1.isBefore(d2);
Remove all occurrences of string w from string s1, and store the result in s2.
var s2 = s1.replaceAll(w,"");
Set n to the number of elements of the list x.
int n = x.length;
Create the set y from the list x.
x may contain duplicates. y is unordered and has no repeated values.
var y = x.toSet();
Remove duplicates from the list x.
Explain if the original order is preserved.
x = x.toSet().toList();
Read an integer value from the standard input into the variable n
String? s = stdin.readLineSync();  
int? n = int.tryParse(s ?? "");
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS.
enum Suit {
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not.
Write the function binarySearch which returns the index of an element having the value x in the sorted array a, or -1 if no such element exists.
measure the duration t, in nanoseconds, of a call to the function foo. Print this duration.
var t = Stopwatch();
print(t.elapsedMicroseconds * 1000);
Write a function foo that returns a string and a boolean value.
foo() => ['a string', true];
Execute f1 if condition c1 is true, or else f2 if condition c2 is true, or else f3 if condition c3 is true.
Don't evaluate a condition when a previous condition was true.
if (c1) {
} else if (c2) {
} else if (c3) {
Run the procedure f, and return the duration of the execution of f.
var s = Stopwatch()..start();
Set boolean ok to true if string word is contained in string s as a substring, even if the case doesn't match, or to false otherwise.
bool ok = s.toUpperCase().contains(word.toUpperCase());
Declare and initialize a new list items, containing 3 elements a, b, c.
var items = [a, b, c];
Remove at most 1 item from list items, having the value x.
This will alter the original list or return a new list, depending on which is more idiomatic.
If there are several occurrences of x in items, remove only one of them. If x is absent, keep items unchanged.
Remove all occurrences of the value x from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
Set the boolean b to true if the string s contains only characters in the range '0'..'9', false otherwise.
final b = RegExp(r'^[0-9]+$').hasMatch(s);
Delete from map m the entry having key k.

Explain what happens if k is not an existing key in m.
Map myMap = {};
Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element.
Assign to string s the hexadecimal representation (base 16) of integer x.

E.g. 999 -> "3e7"
var s = x.toRadixString(16);
Set boolean b to true if file at path fp exists on filesystem; false otherwise.

Beware that you should never do this and then in the next instruction assume the result is still valid, this is a race condition on any multitasking OS.
var b = await File(fp).exists();
Print message msg, prepended by current date and time.

Explain what behavior is idiomatic: to stdout or stderr, and what the date format is.
print('${} msg');
Extract floating point value f from its string representation s
f = num.parse(s);
Create string t from string s, keeping only ASCII characters
var t = '';
for(var c in s.runes) {
  if(c < 128){
    t = t + String.fromCharCode(c);
Remove the last character from the string p, if this character is a forward slash /
if (p.endsWith("/")) p = p.substring(0, p.length - 1);
Remove last character from string p, if this character is the file path separator of current platform.

Note that this also transforms unix root path "/" into the empty string!
if (p.endsWith(path.separator)) p = p.substring(0, p.length - 1);
Create string s containing only the character c.
var s=c;
Create the string t as the concatenation of the string s and the integer i.
var t = '$s$i';
Delete from filesystem the file having path filepath.
Assign to the string s the value of the integer i in 3 decimal digits. Pad with zeros if i < 100. Keep all digits if i1000.
var s = i.toString().padLeft(3,'0');
Initialize a constant planet with string value "Earth".
const String _planet = "Earth";
Multiply all the elements of the list elements by a constant c
elements = [for (var e in elements) e * c];
Alternative implementation:
elements = => e * c).toList();
execute bat if b is a program option and fox if f is a program option.
if (args.contains("b")) bat();
if (args.contains("f")) fox();
Print all the list elements, two by two, assuming list length is even.
for(int i = 0; i < list.length; i += 2) {
  print("${list[i]}, ${list[i + 1]}");
Assign to the variable x the last element of the list items.
x = items.last;
Create the list ab containing all the elements of the list a, followed by all the elements of the list b.
var ab = a + b;
Create the string t consisting of the string s with its prefix p removed (if s starts with p).
var t = s.startsWith(p) ? s.replaceFirst(p,"") : s;
Alternative implementation:
var t = s.startsWith(p) ? s.substring(p.length, s.length) : s;
Assign to the integer n the number of characters of the string s.
Make sure that multibyte characters are properly handled.
n can be different from the number of bytes of s.
int n = s.length;
Set n to the number of elements stored in mymap.

This is not always equal to the map capacity.
var n = mymap.length;
Append the element x to the list s.
Insert value v for key k in map m.
m[k] = v;
Make a HTTP request with method POST to the URL u
await post(u, body: body, headers: headers);
From array a of n bytes, build the equivalent hex string s of 2n digits.
Each byte (256 possible values) is encoded as two hexadecimal characters (16 possible values per digit).
var s = a.buffer
    .map((e) => e.toRadixString(16).padLeft(2, '0'))
From hex string s of 2n digits, build the equivalent array a of n bytes.
Each pair of hexadecimal characters (16 possible values per digit) is decoded into one byte (256 possible values).
var a = hex.decode(s);
Construct a list L that contains all filenames that have the extension ".jpg" , ".jpeg" or ".png" in directory D and all its subdirectories.
var extensions = [".jpg", "jpeg", ".png"];
var L = Directory(D)
    .listSync(recursive: true)
    .where((file) => extensions.contains(p.extension(file.path)))
Set boolean b to true if if the point with coordinates (x,y) is inside the rectangle with coordinates (x1,y1,x2,y2) , or to false otherwise.
Describe if the edges are considered to be inside the rectangle.
var r = Rectangle.fromPoints(Point(x1,y1),Point(x2,y2));
var b = r.containsPoint(Point(x,y));
Return the center c of the rectangle with coördinates(x1,y1,x2,y2)
var r = MutableRectangle.fromPoints(Point(x1, y1), Point(x2, y2));
var center = Point(r.width / 2, r.height / 2);
Create the list x containing the contents of the directory d.

x may contain files and subfolders.
No recursive subfolder listing.
var x = Directory(d).listSync();
Assign to variable t a string representing the day, month and year of the day after the current date.
var now = new;
var t = now.add(new Duration(days: 1));
Schedule the execution of f(42) in 30 seconds.
Future.delayed(const Duration(seconds: 30), () => f(42));
Exit a program cleanly indicating no error to OS
Produce a new list y containing the result of the function T applied to all elements e of the list x that match the predicate P.
var y = x.where(P).map(T).toList();
Given a one-dimensional array a, check if any value is larger than x, and execute the procedure f if that is the case
if (a.any((value) => value > x)) f();
Given an integer array a of size n, pass the first, third, fifth and seventh, ... up to the m th element to a routine foo which sets all these elements to 42.
var a = List.filled(n,0);
foo(List<int> a) {
  a.fillRange(0, a.length, 42);
Retrieve the contents of file at path into a list of strings lines, in which each element is a line of the file.
var lines = File(path).readAsLinesSync();
Abort program execution with error condition x (where x is an integer value)
Truncate a file F at the given file position.
File(F).openSync(mode: FileMode.write).truncateSync(position);
Returns the hypotenuse h of the triangle where the sides adjacent to the square angle have lengths x and y.
var h = sqrt(x * x + y * y);
Calculate the sum of squares s of data, an array of floating point values.
var s = => v * v).reduce((sum, v) => sum + v);
Read an environment variable with the name "FOO" and assign it to the string variable foo. If it does not exist or if the system does not support environment variables, assign a value of "none".
var foo = Platform.environment["FOO"] ?? "none";
Execute different procedures foo, bar, baz and barfl if the string str contains the name of the respective procedure. Do it in a way natural to the language.
var myProc = {"foo": foo, 
              "bar": bar, 
              "baz": baz, 
              "barfl": barfl};

Create the folder at path on the filesystem
Set the boolean b to true if path exists on the filesystem and is a directory; false otherwise.
var b = await Directory(path).exists();
Append extra character c at the end of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
s = s.padRight(m, c);
Prepend extra character c at the beginning of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
s = s.padLeft(m, c);
Create the string t from the value of string s with each sequence of spaces replaced by a single space.

Explain if only the space characters will be replaced, or the other whitespaces as well: tabs, newlines.
var t = s.replaceAll(RegExp(r"\s+"), " ");
Create string t from string s, keeping only digit characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
var t = String.fromCharCodes(
	s.codeUnits.where((x) => (x ^ 0x30) <= 9) );
Set i to the first index in list items at which the element x can be found, or -1 if items does not contain x.
Loop through list items checking a condition. Do something else if no matches are found.

A typical use case is looping through a series of containers looking for one that matches a condition. If found, an item is inserted; otherwise, a new container is created.

These are mostly used as an inner nested loop, and in a location where refactoring inner logic into a separate function reduces clarity.
print(items.any((element) => element == "baz")
    ? "found it"
    : "did not find it");
Insert the element x at the beginning of the list items.
items = [x, ...items];
Declare an optional integer argument x to procedure f, printing out "Present" and its value if it is present, "Not present" otherwise
void f({int? x}) => print(x == null ? "Not present" : "Present");
Remove the last element from the list items.
Create the new list y containing the same elements as the list x.

Subsequent modifications of y must not affect x (except for the contents referenced by the elements themselves if they contain pointers).
y = [...x];
Copy the file at path src to dst.
Print "verbose is true" if the flag -v was passed to the program command line, "verbose is false" otherwise.
print("verbose is ${args.contains("-v")}");
Assign to the string s the standard base64 encoding of the byte array data, as specified by RFC 4648.
var s = base64.encode(data);
Assign to byte array data the bytes represented by the base64 string s, as specified by RFC 4648.
var bytes = base64Decode(s);
Assign to c the result of (a xor b)
var c = a ^ b;
Call a function f on each element e of a set x.
Print the contents of the list or array a on the standard output.
Print the contents of the map m to the standard output: keys and values.
Print the value of object x having custom type T, for log or debug.
Set c to the number of distinct elements in the list items.
var c = items.toSet().length;
Remove all the elements from list x that don't satisfy the predicate p, without allocating a new list.
Keep all the elements that do satisfy p.

For languages that don't have mutable lists, refer to idiom #57 instead.
x.retainWhere((e) => p);
Define variables a, b and c in a concise way.
Explain if they need to have the same type.
var a = 42, b = "Hello", c = 5.0;
Choose a value x from map m.
m must not be empty. Ignore the keys.
var x = m.values.toList()[Random().nextInt(m.length)];
Extract integer value i from its binary string representation s (in radix 2)
E.g. "1101" -> 13
var i = int.parse(s, radix: 2);
Assign to the variable x the string value "a" if calling the function condition returns true, or the value "b" otherwise.
var x = condition() ? "a" : "b";
Replace all exact occurrences of "foo" with "bar" in the string list x
x = => e == 'foo' ? 'bar' : e).toList();
Alternative implementation:
for (var i = 0; i < x.length; i++) {
  if (x[i] == 'foo') x[i] = 'bar';
Print the values of the set x to the standard output.
The order of the elements is irrelevant and is not required to remain the same next time.
Print the numbers 5, 4, ..., 0 (included), one line per number.
for (int i = 5; i >= 0; i--) {
Print each index i and value x from the list items, from the last down to the first.
var i = items.length ;
for (var e in items.reversed) {
  print("$i, $e");
Convert the string values from list a into a list of integers b.
var b =;
Build the list parts consisting of substrings of the input string s, separated by any of the characters ',' (comma), '-' (dash), '_' (underscore).
var parts = s.split( RegExp(r"[,-_]") );
Declare a new list items of string elements, containing zero elements
var items = <String>[];
Alternative implementation:
List<String> items = [];
Assign to t the number of trailing 0 bits in the binary representation of the integer n.

E.g. for n=112, n is 1110000 in base 2 ⇒ t=4
var t = 0;
while (n.isEven && n != 0) {
  n = n >> 1;
Alternative implementation:
t = n.toRadixString(2)
	.takeWhile((e) => e == '0')
Alternative implementation:
t = n.bitLength - 1 - n.toRadixString(2).lastIndexOf('1');
Pass a two-dimensional integer array a to a procedure foo and print the size of the array in each dimension. Do not pass the bounds manually. Call the procedure with a two-dimensional array.
foo(List<List<int>> a) => print("${a.length} ${a[0].length}");
var a = [
    [1, 2],
    [3, 4],
    [5, 6]
Assign to the string s the value of the string v repeated n times, and write it out.

E.g. v="abc", n=5 ⇒ s="abcabcabcabcabc"
var s = v * n;
Declare an argument x to a procedure foo that can be of any type. If the type of the argument is a string, print it, otherwise print "Nothing."

Test by passing "Hello, world!" and 42 to the procedure.
foo(x) => print(x is String ? x : 'Nothing.');

foo('Hello, world!');
Define a type vector containing three floating point numbers x, y, and z. Write a user-defined operator x that calculates the cross product of two vectors a and b.
class Vector {
  final double x, y, z;

  Vector(this.x, this.y, this.z);

  Vector operator *(other) {
    return Vector(y * other.z - z * other.y, 
                  z * other.x - x * other.z,
                  x * other.y - y * other.x);
Given the enumerated type t with 3 possible values: bike, car, horse.
Set the enum value e to one of the allowed values of t.
Set the string s to hold the string representation of e (so, not the ordinal value).
Print s.
var e =;
var s =;
Given a floating point number r1 classify it as follows:
If it is a signaling NaN, print "This is a signaling NaN."
If it is a quiet NaN, print "This s a quiet NaN."
If it is not a NaN, print "This is a number."
if (r1.isNaN) {
  print("This is a quiet NaN.");
} else {
  print("This is a number.");
If a variable x passed to procedure tst is of type foo, print "Same type." If it is of a type that extends foo, print "Extends type." If it is neither, print "Not related."
tst(x) {
  if (x.runtimeType == Foo) {
    print("Same Type.");
  } else if (x is Foo) {
    print("Extends type.");
  } else {
    print("Not related.");
Fizz buzz is a children's counting game, and a trivial programming task used to affirm that a programmer knows the basics of a language: loops, conditions and I/O.

The typical fizz buzz game is to count from 1 to 100, saying each number in turn. When the number is divisible by 3, instead say "Fizz". When the number is divisible by 5, instead say "Buzz". When the number is divisible by both 3 and 5, say "FizzBuzz"
for (int i = 1; i <= 100; i++) {
  var s = StringBuffer();
  if (i % 3 == 0) s.write("Fizz");
  if (i % 5 == 0) s.write("Buzz");
  if (s.isEmpty) s.write(i);
Set the boolean b to true if the directory at filepath p is empty (i.e. doesn't contain any other files and directories)
var b = await Directory(p).list().isEmpty;
Insert an element e into the set x.
Remove the element e from the set x.

Explains what happens if e was already absent from x.
You have a Point with integer coordinates x and y. Create a map m with key type Point (or equivalent) and value type string. Insert "Hello" at position (42, 5).
Map<Point, String> m = {};
m[Point(42, 5)] = "Hello";
Declare a type Foo, and create a new map with Foo as key type.

Mention the conditions on Foo required to make it a possible map key type.
class Foo{};
Map<Foo, int> m = {};
Build the list parts consisting of substrings of input string s, separated by the string sep.
var parts = s.split(sep);
Create a new list a (or array, or slice) of size n, where all elements are integers initialized with the value 0.
var a = List.filled(n, 0);
Print a line "Char i is c" for each character c of the string s, where i is the character index of c in s (not the byte index).

Make sure that multi-byte characters are properly handled, and count for a single character.
s.split('').asMap().forEach((i, c) => print('Char $i is $c'));
Assign to n the number of bytes in the string s.

This can be different from the number of characters. If n includes more bytes than the characters per se (trailing zero, length field, etc.) then explain it. One byte is 8 bits.
var n = utf8.encode(s).length;
Set the boolean b to true if the set x contains the element e, false otherwise.
var b = x.contains(e);
Create the string s by concatenating the strings a and b.
var s = '$a$b';
Alternative implementation:
var s = a + b;
Sort the part of the list items from index i (included) to index j (excluded), in place, using the comparator c.

Elements before i and after j must remain unchanged.
items.setRange(i, j, items.sublist(i, j)..sort(c));
Delete all the elements from index i (included) to index j (excluded) from the list items.
items.removeRange(i, j);
Create a new stack s, push an element x, then pop the element into the variable y.
var s = [];
var y = s.removeLast();
Given an array a containing the three values 1, 12, 42, print out
"1, 12, 42" with a comma and a space after each integer except the last one.
print(a.join(", "));
Given the enumerated type T, create a function TryStrToEnum that takes a string s as input and converts it into an enum value of type T.

Explain whether the conversion is case sensitive or not.
Explain what happens if the conversion fails.
Assign to x2 the value of string x with the last occurrence of y replaced by z.
If y is not contained in x, then x2 has the same value as x.
var position = x.lastIndexOf(y).clamp(0, x.length);
var x2 = x.replaceFirst(y, z, position);
Sort the string list data in a case-insensitive manner.

The sorting must not destroy the original casing of the strings.
data.sort((a, b) => a.toUpperCase().compareTo(b.toUpperCase()));
Create the map y by cloning the map x.

y is a shallow copy, not a deep copy.
var y = Map.of(x);
Write a line of comments.

This line will not be compiled or executed.
// This is a comment
Compute the Fibonacci sequence of n numbers using recursion.

Note that naive recursion is extremely inefficient for this task.
int fibonacci(int n) => n <= 2 ? 1 : fibonacci(n - 2) + fibonacci(n - 1);
Given the integer x = 8, assign to the string s the value "Our sun has 8 planets", where the number 8 was evaluated from x.
var s = "Our sun has $x planets";
Write a function g that behaves like an iterator.
Explain if it can be used directly in a for loop.
List<int> g(int start) sync* {
  while (true) {
    yield start;
Set b to true if the string s is empty, false otherwise
final b = s.isEmpty;
Remove all entries from the map m.

Explain if other references to the same map now see an empty map as well.
Create the list k containing all the keys of the map m
final k = m.keys;
Print the object x in human-friendly JSON format, with newlines and indentation.
var encoded = const JsonEncoder.withIndent('  ').convert(x);
Create the new map c containing all of the (key, value) entries of the two maps a and b.

Explain what happens for keys existing in both a and b.
final c = {...a, ...b};
Create the map m containing all the elements e of the list a, using as key the field
final m = {
  for (final e in a) e,
Compute x = b

b raised to the power of n is equal to the product of n terms b × b × ... × b
final x = b ** n;
Assign to c the value of the last character of the string s.

Explain the type of c, and what happens if s is empty.

Make sure to properly handle multi-bytes characters.
final c = s[s.length - 1];
Determine if the current year is a leap year.
final thisYear =;
final isLeap = DateTime(year, 2, 29).month == 2;