null_safety.dart

/* 
 PRATICAL EXAMPLE 
 - Imagine a school where students take an exam.
 - The exam is out of 20.
 - At the end of the year, the school wants to print out the marks of every student
 - However; not all students took the exam.
*/
class Student {
  late final String
  name; // the late final means we don't give a value to this variable at the time of declaration, but we can give it a value later.
  late final int? marks; //the ?  means we can give it a value , it can be null.
  Student({required this.name, this.marks});
}

void main() {
  List<Student> students = [
    Student(name: 'Alice', marks: 15),
    Student(name: 'sma3il', marks: 0),
    Student(name: "lwahch"),
  ];

  for (var student in students) {
    print(student.name + "'s mark is : " + calculatepercentage(student.marks));
  }
}

String calculatepercentage(int? marks) {
  int the_total_marks = 20;
  double percentage = (marks?.toDouble() ?? 0) * 100 / the_total_marks;
  return marks == null ? "majash lexamen" : percentage.toStringAsFixed(0) + "%";
}