How to set default value for parameter in Dart

To set default values for parameters in Dart , you can use assignment operator (=).

Here in below example we use String prefix = ‘Default’

void printMessage(String message, {String prefix = 'Default'}) {
  print('$prefix: $message');
}

void main() {
  printMessage('Hello'); // Output: Default: Hello

  printMessage('Hi', prefix: 'Custom'); // Output: Custom: Hi
}

Example II

In this example calculateRectangleArea pass two parameters width and height

double calculateRectangleArea({double width = 5.0, double height = 3.0}) {
  return width * height;
}

void main() {
//In this we pass no value so it will use defaut value 
  double area1 = calculateRectangleArea(); // Uses default values (5.0 and 3.0)

//In this we pass width and height output will be different
  double area2 = calculateRectangleArea(width: 8.0, height: 4.0); // Custom values

  print('Area 1: $area1'); // Output: Area 1: 15.0
  print('Area 2: $area2'); // Output: Area 2: 32.0
}