Switch Case in Dart#

Overview#

The switch case in Dart is a control flow statement that allows you to execute one code block from multiple possible cases based on the value of an expression. It provides a cleaner and more organized alternative to multiple if-else statements when dealing with many conditions.

Basic Switch-Case Structure#

The switch statement evaluates an expression and compares its value against multiple case labels. When a match is found, the corresponding code block is executed.

How It Works#

• Evaluation: The switch statement evaluates an expression.
• Matching: It compares the expression’s value to each case label.
• Execution: Executes the block of code associated with the matched case.
• Break: The break statement is used to exit the switch block once a case has been executed, preventing further cases from being executed.
• Default: The default case is optional and runs if no other cases match. It acts like an else in an if-else statement.

Rules and Restrictions#

• The expression in the switch statement must be of type int, String, or an enum.
• Each case must be a constant value.
• Without a break, continue, or return statement in a case block, execution will “fall through” to the next case, which can lead to unintended behavior.

Case and Default Clauses#

• Case Clauses: Define specific values to match against the expression. Each case must be unique and constant.
• Default Clause: Optionally handles any cases not explicitly handled by other case labels. It ensures that there is a fallback option.

Example#

void main() {
  String grade = 'B';

  switch (grade) {
    case 'A':
      print('Excellent');
      break;
    case 'B':
      print('Good');
      break;
    case 'C':
      print('Fair');
      break;
    case 'D':
      print('Poor');
      break;
    default:
      print('Fail');
  }
}

In this example, the output will be “Good” because the grade value is ‘B’.

Switch-Case with Break and Continue#

• Break: Ends the execution of the current case block and exits the switch statement. It prevents the code from “falling through” to subsequent cases.

• Continue: Although not typically used in a switch statement, continue can be employed in loops inside a switch case to skip the rest of the loop’s current iteration.

Example with Break and Continue#

void main() {
  List<int> numbers = [1, 2, 3, 4, 5];
  
  for (int num in numbers) {
    switch (num) {
      case 2:
        print('Number is 2');
        continue; // Skip the rest of the loop for this iteration
      case 4:
        print('Number is 4');
        break; // Exit the switch and loop
      default:
        print('Number is $num');
    }
  }
}

In this example:#

• When num is 2, “Number is 2” is printed, and the loop continues to the next iteration.
• When num is 4, “Number is 4” is printed, and the break statement exits the loop.

Overall#

The switch case in Dart provides a structured way to handle multiple conditions based on a single expression. It simplifies code maintenance by replacing complex if-else chains with a more readable format, and the optional default case ensures there’s always a fallback.