Returning array from function (Syntax Error: Value expected)

Question

Why does the program expect me to return array[c] in the below code when c is the length of array minus 1? I can't seem to follow how my program still manages to execute just well.

P.S I arrived at the last line of code by Trial and Error and it worked as expected. I just don't know how!

 public static int arrayReverse(int[] array)
        {
            int c = array.Length - 1, b;
            for (int i = 0; i < (array.Length / 2); i++)
            {
                b = array[i];
                array[i] = array[c];
                array[c] = b;
                c--;
            }
            return array[c];
        }

My main function looks like this:

 static void Main(string[] args)
        {
            int[] array = new int[] { 1, 5, 3, 4, 2 };
           //Reverse an Array
            arrayReverse(array);
           //Display Array Elements
            foreach (int x in array)
                Console.WriteLine(x);
            Console.ReadLine();
        }

the return value has no use. int[] is reference type and can be modified without return. — Lei Yang
– Lei Yang, Commented Apr 21, 2017 at 6:33
why reinventing the wheel? int[] array = new int[] { 1, 5, 3, 4, 2 }; Array.Reverse(array); — fubo
– fubo, Commented Apr 21, 2017 at 6:36

Sadique · Accepted Answer · 2017-04-21 07:05:14Z

3

Because you are returning an int not an int[]. Here, try this out:

 public static int[] arrayReverse(int[] array)
 {
      int c = array.Length - 1, b;
      for (int i = 0; i < (array.Length / 2); i++)
      {
           b = array[i];
           array[i] = array[c];
           array[c] = b;
           c--;
      }
      return array;
 }

Also, you are not assigning back the returned array in main

array = arrayReverse(array);

Now, you do NOT need to return the array at all, since you are writing elements in place and not allocating new array.

Here, please find the code for In-Place and new array implementations. Debug it - write code on paper try to analyze what is happening.

static void Main(string[] args)
{
    try
    {
        int[] array = new int[] { 1, 5, 3, 4, 2 };

        //Reverse copy of Array
        var newarr = arrayReverseNewArray(array);

        //Display New Array Elements
        foreach (int x in newarr)
            Console.Write(x + ",");

        Console.WriteLine("");

        //Reverse original Array
        arrayReverseinPlace(array);

        //Display original Array Elements
        foreach (int x in array)
            Console.Write(x + ",");
        Console.ReadLine();

    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}


private static void arrayReverseinPlace(int[] array)
{
    for (int i = 0; i < array.Length / 2; i++)
    {
        int tempvar = array[i];
        array[i] = array[array.Length - i - 1];
        array[array.Length - i - 1] = tempvar;
    }
}

private static int[] arrayReverseNewArray(int[] array)
{
    int[] arr = new int[array.Length];
    int j = 0;
    for (int i = array.Length - 1; i >=0 ; i--)
    {
        arr[j] = array[i];
        j++;
    }
    return arr;
}

Here is the Running Sample Code.

edited Apr 21, 2017 at 7:05

answered Apr 21, 2017 at 6:30

Sadique

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10 Comments

Uwe Keim Over a year ago

He also ignores the returned value when calling the function. Probably he needs to read a good tutorial on C#.

Sivarama Krishnan Over a year ago

Thanks! I am wondering why array[c] is okay, but not array[array.length] or array[] ?

Sadique Over a year ago

array[array.length] should work if you return int.array[] is a declaration

Sivarama Krishnan Over a year ago

@UweKeim Sorry about that, I am a novice. Learning by practising. I agree to you that I still need a lot of reading to do. Answering to your question, I made changes to the array directly in the function. I could have just ignored the return type and made the function call as well.

Sivarama Krishnan Over a year ago

@Sadique Well, it gave me a System.IndexOutOfRangeException: 'Index was outside the bounds of the array.' during runtime. I reverted back to ` public static int arrayReverse(int[] array)` because with return type as int[], it does not allow me to return array[array.length] (it then tells me: cannot implicitly convert type int to int[]

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