Control Flow

If Else

Dart has If Else:

if (year >= 2001) {
  print('21st century');
} else if (year >= 1901) {
  print('20th century');
} else {
  print('We Must Go Back!');  
}

Dart also has a ternary if operator:

var foo = true;
print(foo ? 'Foo' : 'Bar'); // Displays "Foo".

While Loop

While loops and do while loops are allowed in Dart:

while(peopleAreClapping()) {
  playSongs();
}

and:

do {
  processRequest();
} while(stillRunning());

Loops can be terminated using a break:

while (true) {
  if (shutDownRequested()) break;
  processIncomingRequests();
}

You can skip iterations in a loop using continue:

for (var i = 0; i < bigNumber; i++) {
  if (i.isEven){
    continue;
  }
  doSomething();
}

For Loop

Two types of for loops are allowed:

for (int month = 1; month <= 12; month++) {
  print(month);
}

and:

for (var object in flybyObjects) {
  print(object);
}

The for-in loop is convenient when simply iterating over an Iterable collection. There is also a forEach method that you can call on Iterable objects that behaves like for-in:

flybyObjects.forEach((object) => print(object));

or, more concisely:

flybyObjects.forEach(print);

Switch Case

Dart has a switch case which can be used instead of long if-else statements:

var command = 'OPEN';

switch (command) {
  case 'CLOSED':
    executeClosed();
    break;
  case 'OPEN':
    executeOpen();
    break;
  case 'APPROVED':
    executeApproved();
    break;
  case 'UNSURE':
    // missing break statement means this case will fall through
    // to the next statement, in this case the default case
  default:
    executeUnknown();
}

You can only compare integer, string, or compile-time constants. The compared objects must be instances of the same class (and not of any of its subtypes), and the class must not override ==.

One surprising aspect of switch in Dart is that non-empty case clauses must end with break, or less commonly, continue, throw, or return. That is, non-empty case clauses cannot fall through. You must explicitly end a non-empty case clause, usually with a break. You will get a static warning if you omit break, continue, throw, or return, and the code will error at that location at runtime.

var command = 'OPEN';
switch (command) {
  case 'OPEN':
    executeOpen();
    // ERROR: Missing break causes an exception to be thrown!!

  case 'CLOSED': // Empty case falls through
  case 'LOCKED':
    executeClosed();
    break;
}

If you want fall-through in a non-empty case, you can use continue and a label:

      var command = 'OPEN';
      switch (command) {
        case 'OPEN':
          executeOpen();
          continue locked;
locked: case 'LOCKED':
          executeClosed();
          break;
      }