How does the code "know" which question to ask? (Improve the Quiz Solution [JavaScript Arrays])

Question

Hey :)
I was wondering how the JavaScript code "knows" which question to ask?
This is the solution code:
// 1. Create a multidimensional array to hold quiz questions and answers
const questions = [
  ['How many planets are in the Solar System?', '8'],
  ['How many continents are there?', '7'],
  ['How many legs does an insect have?', '6'],
  ['What year was JavaScript created?', '1995']
];
// 2. Store the number of questions answered correctly
const correct = [];
const incorrect = [];
let correctAnswers = 0;
/* 
  3. Use a loop to cycle through each question
      - Present each question to the user
      - Compare the user's response to answer in the array
      - If the response matches the answer, the number of correctly
        answered questions increments by 1
*/
for ( let i = 0; i < questions.length; i++ ) {
  let question = questions[i][0];
  let answer = questions[i][1];
  let response = prompt(question);
  if ( response === answer ) {
    correctAnswers++;
    correct.push(question);
  } else {
    incorrect.push(question);
  }
}
I was wondering why JavaScript isn't asking the first question 4 times since, the loop runs for 4 times due to the length of the first array. How does JavaScript "know" to ask the 2nd and 3rd question as well as the 4th?
I hope you understand my question and can help me get my head around this. 
Thanks in advance :)
Cheers
Erik

Rohald van Merode · Accepted Answer

Hi @Erik Biebinger (https://teamtreehouse.com/erikbiebinger), 
Great question! JavaScript knows because you're looping over each of the questions and selecting them one at a time. What is happening in your loop is that the initial value of i is set to 0. The first time your loop runs the first line in the loop is set to let question = questions[0][0]; and the user is prompted to answer the first question. 
After the user has answered that question the loop will go through the next iteration, i will be increased to 1 and therefor the next line will now be let question = questions[1][0];. Selecting the next question / answer in the questions array. 
The loop will repeat this process increasing i by 1 on every iteration until the last question has been asked (until the conditional in the loop i < questions.length; is no longer true. 
Something that helped me tremendously during my learning journey was to log a different values to the console. This will help you to see what your code is doing and gives you a better grasp on the syntax and logic of your code. In this example I would suggest to add some console.log calls in your code and play around with some different values. For example in the loop you could try to console.log(i) or console.log(questions[i]) and console.log(questions[i][0]. 
I hope this has been helpful 🙂

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Erik Biebinger

Erik Biebinger

How does the code "know" which question to ask? (Improve the Quiz Solution [JavaScript Arrays])

1 Answer

Rohald van Merode

Rohald van Merode

Erik Biebinger

Erik Biebinger