grade_report.dart in Dart

Report cards from a const roster, a switch expression, and padding.

// Average each student's scores and print a letter-grade report card.

class Student {
  final String name;
  final List<int> scores;
  const Student(this.name, this.scores);

  double get average =>
      scores.fold(0, (sum, s) => sum + s) / scores.length;
}

const roster = [
  Student('Ada', [92, 88, 97]),
  Student('Grace', [84, 91, 78]),
  Student('Alan', [70, 66, 74]),
  Student('Edsger', [58, 67, 61]),
];

String letter(double avg) => switch (avg) {
      >= 90 => 'A',
      >= 80 => 'B',
      >= 70 => 'C',
      >= 60 => 'D',
      _ => 'F',
    };

void main() {
  final sorted = [...roster]..sort((a, b) => a.name.compareTo(b.name));
  print('student  avg grade');
  for (final s in sorted) {
    final name = s.name.padRight(8);
    final avg = s.average.toStringAsFixed(1).padLeft(4);
    print('$name $avg  ${letter(s.average)}');
  }
  final all = roster.expand((s) => s.scores).toList();
  final classAvg = all.fold(0, (sum, s) => sum + s) / all.length;
  print('Class average: ${classAvg.toStringAsFixed(1)}');
}

How it works

1. Student computes its average with a fold getter.
2. letter maps averages to grades with relational patterns.
3. expand pools every score for the class average.

Keywords and builtins used here

• String
• Student
• class
• const
• double
• final
• for
• get
• in
• int
• switch
• this
• void

The run, in numbers

Lines

38

Characters to type

954

Tokens

341

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 315 seconds.

Type this snippet

Step 2 of 3 in Encore, step 26 of 27 in Language basics.

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