Why are variable not recognised from inside for-statements?

Question

What I am trying to do is create an array that pulls even numbers from another array. I'm not sure if I have gone about it the right way. I've look for ways of returning from statements like you would functions/methods and I can't find anything, not even sure if it is possible.

Anyway, the issue I am having here is the 'return evenArray' below 'cannot find symbol.' I am not sure what this means?

public static int[] getEvenArray(int[] array)
{        
    int dividedBy = 2;
    int evenElement;
    int evenCount = 0;

    for(int i = 0; i < array.length; i++)
    {
        int[] evenArray;
        evenElement = array[i] % dividedBy;

        if(evenElement == 0)
        {
            evenCount++;
        }
        else
        {
            array[i] = 0;
        }

        evenArray = new int[evenCount];

        for(int x = 0; x < evenArray.length; x++)
        {
            if(array[i] != 0)
            {
                evenArray[x] = array[i];
            }
        }
    }

    return evenArray;
}

This is for a tutorial from one of my lectures, it's a little bit challenging to say the least :-)0

Either this isn't C++ (it looks more like Java), or it has far more errors than trying to access a variable outside its scope. In any case, you need to move the declaration of `evenArray` outside the for loop, for it to be accessible there. — Mike Seymour, Nov 19 '14 at 12:36
I'll have to go over that shortly, thank you for pointing these issues out though Raphael :-) — Ryan 'Maverick' Buxton, Nov 19 '14 at 12:43
It is Java, not C++, I was doing some other C++ stuff this morning and must have got it all muddled up... Sorry guys :/ — Ryan 'Maverick' Buxton, Nov 19 '14 at 12:44

score 3 · Answer 1 · answered Nov 19 '14 at 12:29

3

evenArray is defined within the scope of the for loop. (Actually a little worse than that; you're redeclaring it on each iteration so discarding the previous contents).

So once you're outside the for loop you can't refer to it.

Quickest fix is to use a std::vector<int> for this type, and declare it at the start of the function. Also change the return type of the function to the same. Don't forget to size the vector appropriately.

(Moving on, a smart lecturer will ask you about returning a std::vector which could potentially take a deep copy of that vector. Pre C++11 you'd mention return value optimisation, now you can talk about r-value references. No deep copy will be taken since the move constructor will be used).

answered Nov 19 '14 at 12:29

Bathsheba

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I moved 'int[] evenArray;' before the for-loop and then I get the 'not be initialised' error but it has been initialised inside the for-loop. Is the issue because it's initialisation is within the scope of the for-loop that 'return evenArray;' can't see the initialisation? – Ryan 'Maverick' Buxton Nov 19 '14 at 12:33
Use a `std::vector` unless you've specifically been asked not to. – Bathsheba Nov 19 '14 at 12:33
@Bathsheba: To do that, you'll have to first rewrite the code in C++. – Mike Seymour Nov 19 '14 at 12:40
My apologies, mix up. I was doing C++ earlier this morning :/ it is indeed Java – Ryan 'Maverick' Buxton Nov 19 '14 at 12:45

score 0 · Answer 2 · answered Nov 19 '14 at 12:31

0

Variable declared inside a block is not visible outside of it; move this int[] evenArray; to very start of function.

answered Nov 19 '14 at 12:31

Ali Kazmi

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Why are variable not recognised from inside for-statements?

2 Answers2