Example of Class, Object, Constructor, Method, Input From User

 import "dart:io";

class Mathematics {
  var a,b,c,d,e,f,g,r;
  Mathematics(double x, double y) {
    a = x;
    b = y;
  }
  // void getData(double x, double y) {
  //   a = x;
  //   b = y;
  // }

  void Circumference() {
    double ans = (3.14 * a * a);
    print(ans);
  }
  double Formula() {
    c = ((a + b)*(a+b)*(a+b));

    return c;
  }
  double calculate() {
    // a^2 - b^2 = (a+b)(a-b);
    d = (a + b)*(a - b);
    return d;
  }

}
void main() {
  // Mathematics math = new Mathematics();

  print("Please Enter value of r: ");
  double i =double.parse(stdin.readLineSync()!);
  print("Please Enter value of a: ");
  double o = double.parse(stdin.readLineSync()!);
  print("Please Enter value of b: ");
  double p = double.parse(stdin.readLineSync()!);
  // math.getData(i, o);
  Mathematics math = new Mathematics(i,o);

  math.Circumference();
  print(math.Formula());
  print(math.calculate());

}