Dart switch

Summary: in this tutorial, you’ll learn how to use the Dart switch statement to do something when an expression equals a value.

Introduction to the Dart switch statement

The switch statement evaluates an expression and compares its result with a value in a set. If they are equal, the switch statement will execute the statement in the matching case branch.

Internally, the switch statement uses the comparison operator (==) to compare integer, string, enumeration, or compile-time constants.

The following illustrates the syntax of the switch statement:

switch (expression)
{
    case value1:
        // statement1;
        break;
    case value2:
        // statement2;
        break;
    case value3:
        // statement3;
        break;
    default:
        // statementn;
        break;
}Code language: Dart (dart)

In this syntax, the switch statement compares the result of the expression with value1, value2, value3, … in each case clause from top to bottom.

If the result of the expression equals a value, the switch statement executes the statement in the matched case branch.

If the expression doesn’t equal any value, the switch statement executes the statement in the default branch.

The default clause is optional. If you omit it and the expression doesn’t match any value, the switch statement doesn’t execute any statement and passes the control to the statement after it.

The following flowchart illustrates how the switch statement works:

Dart switch statement example

The following program uses the switch statement to display the day name based on the day number:

void main() {
  int dayNumber = 3;
  String dayName = "";

  switch (dayNumber) {
    case 1:
      dayName = "Sunday";
      break;
    case 2:
      dayName = "Monday";
      break;
    case 3:
      dayName = "Tuesday";
      break;
    case 4:
      dayName = "Wednesday";
      break;
    case 5:
      dayName = "Thursday";
      break;
    case 6:
      dayName = "Friday";
      break;
    case 7:
      dayName = "Saturday";
      break;
    default:
      dayName = "Invalid day";
      break;
  }
  print(dayName);
}
Code language: Dart (dart)

How it works.

First, declare the variable dayNumber and initialize its value to 3. Also declare the variable dayName and initialize its values to an empty string:

int dayNumber = 3;
String dayName = "";Code language: JavaScript (javascript)

Second, use a switch statement to assign a day name to the dayName variable based on the value of the dayNumber:

switch (dayNumber) {
    case 1:
      dayName = "Sunday";
      break;
    case 2:
      dayName = "Monday";
      break;
    case 3:
      dayName = "Tuesday";
      break;
    case 4:
      dayName = "Wednesday";
      break;
    case 5:
      dayName = "Thursday";
      break;
    case 6:
      dayName = "Friday";
      break;
    case 7:
      dayName = "Saturday";
      break;
    default:
      dayName = "Invalid day";
      break;
  }Code language: JavaScript (javascript)

Third, display the value of the day name.

In this example, the dayNumber is 3. Therefore, the switch statement assigns the string "Tuesday" to the dayName.

If you change the dayNumber to a value that is not between 1 and 7, the switch statement will execute the default branch that assigns the "Invalid day" to the dayName:

Dart switch statement with group cases

If you want to execute the same statement based on multiple values, you can group cases as follows:

switch (expression)
{

    case value1:
    case value2:
        // statement1
        break;

    case value3:
    case value4:
        // statement2
        break;
    default:
        // statement3
        break;

}Code language: Dart (dart)

In this syntax, the switch statement will execute statement1 if the result of the expression equals the value1 or value2. Similarly, it’ll execute the statement2 if the result of the expression equals the value3 and value4.

If the result of the expression doesn’t equal any values in the case clauses, it’ll execute the statment n in the default clause.

The following example uses the switch statement with group cases to determine whether a day is a weekday or weekend:

void main() {
  String dayName = "Monday";
  String day = "";

  switch (dayName) {
    case "Monday":
    case "Tuesday":
    case "Wednesday":
    case "Thursday":
    case "Friday":
      day = "Weekday";
      break;
    case "Saturday":
    case "Sunday":
      day = "Weekend";
      break;
    default:
      day = "Invalid";
  }

  print(day);
}Code language: Dart (dart)

How it works.

First, declare the dayName variable and initialize it with the string "Monday":

String dayName = "Monday";Code language: Dart (dart)

Second, use a switch statement with group cases to determine if the day name is a weekday or weekend. If the dayName is from Monday to Friday, assign the "Weekday" to the day variable.

If the day is Saturday or Sunday, assign the "Weekend" to the day variable. If the day is not from Monday to Sunday, assing "invalid" to the day in the default branch.

String day = "";
switch (dayName) {
    case "Monday":
    case "Tuesday":
    case "Wednesday":
    case "Thursday":
    case "Friday":
      day = "Weekday";
      break;
    case "Saturday":
    case "Sunday":
      day = "Weekend";
      break;
    default:
      day = "Invalid";
      break;
  }Code language: Dart (dart)

Third, display the value of the day variable:

print(day);Code language: Dart (dart)

Summary

• Use the switch statement to execute a block if the result of an expression equals a value.
• If the expression doesn’t equal any value in a set, the switch statement will execute the default branch. The default branch is optional.
• The switch statement uses the comparison operator (==) to compare integers, strings, and constants.
• Use group cases to execute the same statement that corresponds to multiple values.