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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Build a Quiz Challenge, Part 1 Solution

Posted by Nelson Lourenco
Nelson Lourenco
1,766 Points

Simpler solution, why not rendering?

So this is my solution which seems to not be outputting the number correct.

var quiz = [
  ['What color are Gala apples?', 'Red'],
  ['What brand of phone do Koreans make?', 'Samsung'],
  ['What type of bird is a Macaw?', 'Parrot']
];

var numCorrect = 0;
var question;
var answer;

for ( var i = 0; i <= quiz.length; i += 1 ) {
  var question = prompt(quiz[i][0]); /* response becomes new question value */
  var answer = quiz[i][1];
  if ( question === answer ) {
    numCorrect += 1;
  }
}

document.write('You have answered ' + numCorrect + ' questions correct.');

In this example, instead of having a variable called 'response' I transferred the user response value over to that specific question and made a conditional based on that ( question ==== answer).

Can anybody tell me why the console is telling me that 'quiz[i]' is undefined?

1 Answer

Unsubscribed User
Unsubscribed User
6,144 Points

Your for condition should look like this : 

  for ( var i = 0; i < quiz.length; i += 1)

It took me some time to figure it out.

Nelson Lourenco
Nelson Lourenco
1,766 Points

awesome, I'm happy to find out that was all I needed!! Thanks for pointing that out to me.

I'm curious why it still wouldn't work though, especially since less than (<) occurs before equal to (=) ?

Unsubscribed User
Unsubscribed User
6,144 Points

The quiz array got 3 elements in it but the 3 elements = quiz[0], quiz[1], quiz[2]. When you use the

  <=

It will try to search for a quiz[3] (because quiz.length = 3) but this one is undefined because it doesn't exist.

Is it clear ? It's pretty hard for me to explain this in english.

Nelson Lourenco
Nelson Lourenco
1,766 Points

Yeah I understand it, thanks. I am confusing the 'length' of var quiz (3) with the 'index position' of the last array (2). Since the loop executes on quiz[0], the program was looking for a forth array aka quiz[3].

quiz[0]
1 <= 3 (true)
quiz[1]
2 <= 3 (true)
quiz[2]
3 <= 3 (true)
quiz[3] ?undefined?
4 <= 3 (false)
Unsubscribed User
Unsubscribed User
6,144 Points

Yes this is it, it begins with 0 and quiz[3] doesn't exist so the console returns undefined.