`Int` arrays

Int arrays are common: they store many integer values. These values can be used in many ways—ints can refer to indexes in other collections, or measurements from the real world.

Elements in an int array are stored together. This improves locality of reference when looping over the values—loops are fast on int arrays.

This example shows how to declare int arrays. The first 3 are declared on single lines, while the fourth array is declared by individual assignment of the elements.

And The message will be written to the console because the first element of each array is identical in value.

Note The first array element is at index 0. This is true in C# but not in VB.NET.

using System;

// Declare int arrays.
int[] arr1 = new int[] { 3, 4, 5 };
int[] arr2 = { 3, 4, 5 };
var arr3 = new int[] { 3, 4, 5 };

// Declare int array of zeros.
int[] arr4 = new int[3];            
arr4[0] = 3;
arr4[1] = 4;
arr4[2] = 5;

if (arr1[0] == arr2[0] && arr1[0] == arr3[0] && arr1[0] == arr4[0])
{
    Console.WriteLine("First elements are the same");
}
First elements are the same

Empty

Here we see two ways to create an int array with zero elements. An empty initializer expression can be used. Or we can specify a length of 0.

using System;

// This is a zero-element int array.
var values1 = new int[] { };
Console.WriteLine(values1.Length);

// This is a zero-element int array also.
var values2 = new int[0];
Console.WriteLine(values2.Length);0
0

Example 2

We can use int arrays in loops. The example shows the foreach-loop, which has simpler syntax, and the for-loop, which gives you more control and possibly greater performance.

Here The Main method calls the GetEmployeeIds method twice. The ints in the int array are looped over with foreach.

Tip GetEmployeeIds shows how to return an int array from a method in the C# language.

Tip 2 You never have to add code to free the memory for the int array result—it is garbage-collected.

using System;

class Program
{
    static void Main()
    {
        // Loop over array of integers.
        foreach (int id in GetEmployeeIds())
        {
            Console.WriteLine(id);
        }
        // Loop over array of integers.
        int[] employees = GetEmployeeIds();
        for (int i = 0; i < employees.Length; i++)
        {
            Console.WriteLine(employees[i]);
        }
    }

    /// <summary>
    /// Returns an array of integers.
    /// </summary>
    static int[] GetEmployeeIds()
    {
        int[] employees = new int[5];
        employees[0] = 1;
        employees[1] = 3;
        employees[2] = 5;
        employees[3] = 7;
        employees[4] = 8;
        return employees;
    }
}1
3
5
7
8
1
3
5
7
8

Example 3

Next we use int arrays in an object-oriented program design. The Employee class here stores an internal reference to an int array at the class level.

Here The code initializes a new int array with 3 elements. This stores the team numbers that the employee belongs to.

And The int array here exists only in one place. The Employee constructor accepts a reference to an int array.

Tip No element copying is done, making this code fast. Only the array reference itself (4 or 8 bytes) is copied.

using System;

class Program
{
    static void Main()
    {
        // Declare new int array.
        int[] teams = new int[3];
        teams[0] = 1;
        teams[1] = 2;
        teams[2] = 3;

        // New employee that stores int array reference.
        Employee employee = new Employee(teams);

        // Loop through each int in employee's class.
        foreach (int team in employee.Teams)
        {
            Console.WriteLine(team);
        }
    }
}

/// <summary>
/// Stores an employee and his teams.
/// </summary>
class Employee
{
    /// <summary>
    /// Int array reference at class level.
    /// </summary>
    int[] _teams;

    /// <summary>
    /// Create new employee.
    /// </summary>
    /// <param name="teams">Teams for the employee.</param>
    public Employee(int[] teams)
    {
        _teams = teams;
    }

    /// <summary>
    /// Get array of teams.
    /// </summary>
    public int[] Teams
    {
        get
        {
            return _teams;
        }
    }
}1
2
3

Discussion

An array in the C# language is a reference type. This means it refers to another object and doesn't contain the raw data.

Summary