Previous lesson starts with one-dimensional array. In this lesson we’ll review arrays more closely.

Agenda

foreach
Find maximum element of array
Sum of array elements
Two-dimentional arrays
Bubble sorting
References

foreach

Performs the specified action for each element in an array.

Following example shows how to handle array with foreach loop.

var words = new[] {"Hey", "dude", "where", "is", "my", "car", "?"};
int numberOfWords = 0;
foreach (var word in words)
{
    Console.Write($"{word} ");
    numberOfWords++;
}
Console.WriteLine();
Console.WriteLine($"It has {numberOfWords} words.");

It takes array elements one by one, prints it and increments counter inside a loop’s body.

Find maximum element of array

Such simple task can be completed with for loop as well as with for loop.

Let’s try it with foreach first.

var array = new[] { 3, 5, 3, 99, 6, 5, 5, 4, 4, 43, 2, 0 };

var maxElement = array[0];//Why we need it?
foreach (var currentItem in array)
{
    if (currentItem > maxElement)
    {
        maxElement = currentItem;
    }
}

Console.WriteLine($"Maximum element of array is {maxElement}");

And now I’ll show you how ‘for’ can be better for this in case you need more functionality rather than just find some element.

var array = new[] { 3, 5, 3, 99, 6, 5, 5, 4, 4, 43, 2, 0 };

var maxElement = array[0];//Why we need it?
var maxElementPosition = 0;
for (int i = 0; i < array.Length; i++)
{
    var currentItem = array[i];
    if (currentItem > maxElement)
    {
        maxElement = currentItem;
        maxElementPosition = i;
    }
}

Console.WriteLine($"Maximum element of array is {maxElement}");
Console.WriteLine($"Maximum element position is {maxElementPosition}");

This example demonstrates that you can not only find the maximum element but its index as well.

Two-dimentional arrays

Actually it’s just a matrix. E.g.:

in C# 2d array I.e. matrix can be defined as:

var matrix = new[,]
{
  {3, 5, 3, 2, 6},
  {3, 5, 3, 2, 6},
  {3, 5, 3, 2, 6},
  {3, 5, 3, 2, 6},
  {3, 5, 3, 2, 6},
};

Sum of array elements

Let’s review an example how to sum 2d array.

var array2d = new[,]
{
    {1, 5},
    {2, 4},
    {7, 3}
};

var sum = 0;

for (int i = 0; i < array2d.GetLength(0); i++)
{
    for (int j = 0; j < array2d.GetLength(1); j++)
    {
        sum += array2d[i, j];
    }
}
Console.WriteLine($"Array sum is: {sum}");

Now, let’s try to sum main diagonal elements of 5*5 matrix.

var array2d = new[,]
{
    {3, 5, 3, 2, 6},
    {3, 0, 48, 2, 6},
    {3, 5, 7, 2, 6},
    {3, 5, 3, 2, 6},
    {3, 5, 3, 2, 34}
};

var sum = 0;

//diagonals sum
for (int i = 0; i < array2d.GetLength(0); i++)
{
    sum += array2d[i, i];
}
Console.WriteLine($"Diagonal sum is: {sum}");

Well, now let’s calculate both diagonals.

var array2d = new[,]
{
    {3, 5, 3, 2, 6},
    {3, 5, 48, 2, 6},
    {3, 5, 7, 2, 6},
    {3, 5, 3, 2, 6},
    {3, 5, 3, 2, 34}
};

var sum = 0;

for (int mainIndex = 0; mainIndex < array2d.GetLength(0); mainIndex++)
{
    var secondaryIndex = array2d.GetLength(0) - 1 - mainIndex;

    sum += array2d[mainIndex, secondaryIndex];

    //preventing common diagonals crossing item '7' to be summed twice
    if (secondaryIndex != mainIndex)
    {
        sum += array2d[mainIndex, mainIndex];
    }
}

Console.WriteLine($"Diagonals sum is: {sum}");

Bubble sorting

This task can be done with for loop.

var array = new[] { 3, 5, 3, 2, 6, 5, 5, 4, 4, 34, 2, 0 };

Console.WriteLine("Initial array:");
Console.WriteLine(string.Join(",", array));

for (int i = 0; i < array.Length; i++)
{
    for (int j = i; j < array.Length - 1; j++)
    {
        if (array[j] > array[j + 1])
        {
            int t = array[j];
            array[j] = array[j + 1];
            array[j + 1] = t;
        }
    }
}

Console.WriteLine("Sorted array:");
Console.WriteLine(string.Join(",", array));

for and foreach benefits: