Comparing two char arrays and creating an Int array of the index of values that do not match up

Question

I have two char arrays. One is the correct answers to the exam, char[] answers and the other is the char[] studentAnswers. I want to compare the two arrays and if there is an incorrect answer I want to store what questions they got wrong.

questionsMissed = i
questionsMissed = studentAnswers[i]

public int[] questionsMissed(char[] studentAnswers)
{
  for(int i = 0; i<studentAnswers.length; i++){
    if(studentAnswers[i] != answers[i]){
      questionsMissed =;
    }
  }
  return questionsMissed;
}

I want questionMissed to store the index of the char values that do not match.

Then simply allocate a new array of the same size as the number of questions. All you need to to do is store a 1 in the proper slot for that value of i if they got the question wrong or a 0 if they got it correct. — WJS
– WJS, Commented Oct 16, 2019 at 16:17

Ryuzaki L · Accepted Answer · 2019-10-16 16:40:32Z

1

Probably you need a List of Integer to add indexes and then convert it into int array

public int[] questionsMissed(char[] studentAnswers) {

List<Integer> list = new ArrayList<>();

for(int i = 0; i<studentAnswers.length; i++){
   if(studentAnswers[i] != answers[i]){
      list.add(i);
     }
   }
 return list.stream().mapToInt(Integer::intValue).toArray();
}

You can do this easily by using java-8 stream

int[] res = IntStream.range(0, studentAnswers.length)
                     .filter(i->studentAnswers[i] != answers[i])
                     .toArray();

If you you are on java-7 you need to iterate the list again

public int[] questionsMissed(char[] studentAnswers) {

List<Integer> list = new ArrayList<>();

for(int i = 0; i<studentAnswers.length; i++){
   if(studentAnswers[i] != answers[i]){
      list.add(i);
     }
   }
    int[] arr = new int[list.size()];

    for(int i=0; i<arr.length; i++) {
        arr[i]=list.get(i);
    }
  return arr;
}

edited Oct 16, 2019 at 16:40

answered Oct 16, 2019 at 16:18

Ryuzaki L

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3 Comments

Ross Over a year ago

I have not learned java-8 stream yet as in my classes we have not gotten that far. Can you provide any answer without using this.

Ross Over a year ago

When I ran that it referenced the memory where it was stored and not the index of the incorrect question. This is what the textbook ask for. questionsMissed. An int array containing the question numbers of the questions that the student missed

Ryuzaki L Over a year ago

Sorry i did not get your question @Ross

Jaideep Shekhar · Accepted Answer · 2019-10-16 17:07:19Z

1

It is easier if you use a list to append the indexes and return an int array at the end:

public int[] questionsMissed(char[] studentAnswers)
{
  List<Integer> questionsMissed  = new ArrayList<>();
  for(int i = 0; i<studentAnswers.length; i++){
    if(studentAnswers[i] != answers[i]){
      questionsMissed.add(i);
    }
  }
  return questionsMissed.toArray();
}

edited Oct 16, 2019 at 17:07

Jaideep Shekhar

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answered Oct 16, 2019 at 16:19

NiVeR

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1 Comment

Ryuzaki L Over a year ago

List.toArray() returns object but not int array

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