Here's my answer:

int[] z = new List<string>()
    .Concat(a)
    .Concat(b)
    .Concat(c)
    .ToArray();

This method can be used at initialization level, for example to define a static concatenation of static arrays:

public static int[] a = new int [] { 1, 2, 3, 4, 5 };
public static int[] b = new int [] { 6, 7, 8 };
public static int[] c = new int [] { 9, 10 };

public static int[] z = new List<string>()
    .Concat(a)
    .Concat(b)
    .Concat(c)
    .ToArray();

However, it comes with two caveats that you need to consider:

• The Concat method creates an iterator over both arrays: it does not create a new array, thus being efficient in terms of memory used: however, the subsequent ToArray  will negate such advantage, since it will actually create a new array and take up the memory for the new array.
• As @Jodrell said, Concat would be rather inefficient for large arrays: it should only be used for medium-sized arrays.

If aiming for performance is a must, the following method can be used instead:

/// <summary>
/// Concatenates two or more arrays into a single one.
/// </summary>
public static T[] Concat<T>(params T[][] arrays)
{
    // return (from array in arrays from arr in array select arr).ToArray();

    var result = new T[arrays.Sum(a => a.Length)];
    int offset = 0;
    for (int x = 0; x < arrays.Length; x++)
    {
        arrays[x].CopyTo(result, offset);
        offset += arrays[x].Length;
    }
    return result;
}

Or (for one-liners fans):

int[] z = (from arrays in new[] { a, b, c } from arr in arrays select arr).ToArray();

Although the latter method is much more elegant, the former one is definitely better for performance.

For additional info, please refer to this post on my blog.

Try the following:

T[] r1 = new T[size1];
T[] r2 = new T[size2];

List<T> targetList = new List<T>(r1);
targetList.Concat(r2);
T[] targetArray = targetList.ToArray();

I think a list would be apt for this purpose.

You can create a list like this.

List<int> Items = new List<int>();  

Then you can pretty easily just use a for each loop to iterate over any number of arrays and add them to the list.

foreach (int i in nameOfArray)
{
    Items.Add(i); 
}

If you use a list it would remove the problem of an out of bounds exception. A list can be used for all the same functionality as an array. The only meaningful difference is the lack of a hard limit in the number of items.

int[] scores = { 100, 90, 90, 80, 75, 60 };
int[] alice = { 50, 65, 77, 90, 102 };
int[] scoreBoard = new int[scores.Length + alice.Length];

int j = 0;
for (int i=0;i<(scores.Length+alice.Length);i++)  // to combine two arrays
{
    if(i<scores.Length)
    {
        scoreBoard[i] = scores[i];
    }
    else
    {
        scoreBoard[i] = alice[j];
        j = j + 1;

    }
}


for (int l = 0; l < (scores.Length + alice.Length); l++)
{
    Console.WriteLine(scoreBoard[l]);
}