Score calculation
- Dart course
- Intermediate
- Lesson 39/116
- 6 min
Learn correct count with the score calculation method.
Score tracking
To evaluate the quiz we write a grade method. It compares a given answer list with the question answers and writes the correct count to the score field. Then it prints the score.
The Quiz class gets an int score = 0; field. The grade(List<String> answers) method compares each answer with questions[i].answer; if equal it runs score++.
This structure is the basis of automatic answer evaluation. Real apps read answers from the user; here we simulate with a fixed list.
Showing the result
After the loop the grade method prints the result with print('Score: $score'). If one of two answers is correct the output is Score: 1.
$score is string interpolation; it embeds the score variable value into the text. In Dart $variable gives the variable value.
When this method is called the quiz is evaluated. The next lesson combines all pieces into a working app.
Practice Add the grade method and score field
Add an int score = 0 field to the Quiz class. Then write void grade(List<String> answers): start with score = 0, loop with for to compare each answer with questions[i].answer, run score++ on a match. After the loop write print('Score: $score'). The main already calls quiz.grade(['Ankara', 'Wrong']).
Starter code
class Question {
String text;
String answer;
Question(this.text, this.answer);
}
class Quiz {
List<Question> questions = [];
// add the score field
void addQuestion(Question q) {
questions.add(q);
}
void play() {
for (var i = 0; i < questions.length; i++) {
print('${i + 1}. ${questions[i].text}');
}
}
// add the grade method
}
void main() {
var quiz = Quiz();
quiz.addQuestion(Question('What is the capital?', 'Ankara'));
quiz.addQuestion(Question('How many days in a week?', '7'));
quiz.grade(['Ankara', 'Wrong']);
}Sample solution
class Question {
String text;
String answer;
Question(this.text, this.answer);
}
class Quiz {
List<Question> questions = [];
int score = 0;
void addQuestion(Question q) {
questions.add(q);
}
void play() {
for (var i = 0; i < questions.length; i++) {
print('${i + 1}. ${questions[i].text}');
}
}
void grade(List<String> answers) {
score = 0;
for (var i = 0; i < questions.length; i++) {
if (answers[i] == questions[i].answer) {
score++;
}
}
print('Score: $score');
}
}
void main() {
var quiz = Quiz();
quiz.addQuestion(Question('What is the capital?', 'Ankara'));
quiz.addQuestion(Question('How many days in a week?', '7'));
quiz.grade(['Ankara', 'Wrong']);
}Expected output
Score: 1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the score parts
| Term | Meaning |
|---|---|
int score = 0 |
Score field |
grade(List<String> answers) |
Grading method |
answers[i] == questions[i].answer |
Comparison |
score++ |
Correct count increment |
2 When is answers[i] == questions[i].answer true?
if (answers[i] == questions[i].answer) {
score++;
}- When the answer is empty
- When the answer is wrong
- When the given answer matches the correct one Correct answer
- As many times as questions
Explanation: the condition holds when the given answer equals the correct one.
3 Score increment
void grade(List<String> answers) {
score = 0;
for (var i = 0; i < questions.length; i++) {
if (answers[i] == questions[i].answer) {
____;
}
}
print('Score: $score');
}void grade(List<String> answers) {
score = 0;
for (var i = 0; i < questions.length; i++) {
if (answers[i] == questions[i].answer) {
score++;
}
}
print('Score: $score');
}Explanation: score++ raises the correct count by one.