structure Constant in Dart

In Dart, a constant is a variable whose value cannot be changed once it is assigned. Constants are useful when you want to ensure that a value never changes throughout the execution of your program.

Here are some examples of how to use constants in Dart:

1. Declaring a constant integer:

const int num = 10;

Here, num is a constant integer whose value is 10.

2. Declaring a constant string:

const String message = "Hello, world!";

Here, message is a constant string whose value is "Hello, world!".

3. Using a constant in an expression:

const int a = 5;
const int b = 10;
const int result = a + b;
print(result); // Output: 15

Here, a and b are constants, and we use them in an expression to compute the value of result.

4. Using constants with classes:

class Circle {
  final double radius;
  const Circle(this.radius);
  
  double get area => 3.14 * radius * radius;
}
void main() {

  const c = Circle(2.5);

  print(c.area); // Output: 19.625

}

Here, we define a Circle class with a radius property that is marked as final. We also mark the constructor as const, which means that instances of Circle are immutable and can be used as constants. We create a constant Circle object c with a radius of 2.5, and then use its area property to compute the area of the circle.