A Class to Manage Arrays

Introduction

To assist with the use and management of arrays, you can combine the array features of the C# language and support from the .NET Framework. As mentioned already, to support arrays, the .NET Framework provides the Array class that is defined in the System namespace of the mscorlib.dll assembly.

When you create an array in C# code, whether an array of primitive values or an array of objects, you are in fact declaring a variable of type Array. Based on this, since an array variable is an object of a class type, you can use the characteristics of the Array class to create an array and/or to manipulate the values stored in the variable. You can create an array using any of the techniques we saw in the previous lessons, or you can use the Array class.

Practical LearningPractical Learning: Introducing Arrays and Classes

  1. Start Microsoft Visual Studio
  2. On the main menu, click File -> New -> Project...
  3. In the middle list, click Console App (.NET Framework)
  4. Change the Name of the project to CountriesStatistics2
  5. Click OK
  6. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> New Item...
  7. In the left frame of the Add New Item dialog box, click Code and, in the middle frame, click Interface
  8. Change the Name to Abbreviated
  9. Click Add
  10. Create a string-based property as follows: 
    namespace CountriesStatistics2
{
    interface IAbbreviated
    {
        string Abbreviation { get; set; }
    }
}
  11. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> New Item
  12. In the middle list of the dialog box, make sure Interface is selectd. Change the Name to GovernmentEntity
  13. Click Add
  14. Change the class as follows: 
    namespace CountriesStatistics2
{
    interface IGovernmentEntity
    {
        string Name    { get; set; }
        int    Area    { get;      }
        string Capital { get; set; }
    }
}
  15. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> Class...
  16. Type Region as the Name of the class
  17. Click Add
  18. Change the document as follows: 
    namespace CountriesStatistics2
{
    public class Region
    {
        public string Designation { get; set; }
        public string Description { get; set; }
    }
}
  19. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> Class...
  20. Type State as the name of the file
  21. Press Enter
  22. Change the class as follows: 
    namespace CountriesStatistics2
{
    public class State : IGovernmentEntity,
                         IAbbreviated
    {
        // From the IAbbreviated interface
        public string Abbreviation { get; set; }

        // From the IGovernmentEntity interface
        public string Name { get; set; }
        public int Area { get; set; }
        public string Capital { get; set; }

        // New Properties
        public string StateName => Name;
        public int AreaSqrMiles => Area;

        public int AreaSqrKms { get; set; }
        public Region Region { get; set; }

        public override bool Equals(object obj)
        {
            State stt = (State)obj;

            if (stt.Name == Name)
                return true;

            return false;
        }

        public override int GetHashCode()
        {
            return base.GetHashCode();
        }
    }
}
  23. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> Class...
  24. Type Federation
  25. Click Add
  26. Change the class as follows: 
    namespace CountriesStatistics2
{
    public class Federation : State
    {
        public string AdmissionUnionDate  { get; set; }
        public int      AdmissionUnionOrder { get; set; }
    }
}
  27. In the Solution Explorer, right-click CountriesStatistics2 -> Add -> Class...
  28. Type UnitedStates as the name of the class
  29. Click Add

Creating an Array

To assist you with creating an array, the Array class is equipped with a method named CreateInstance() that comes in various versions. To create a one-dimensional array whose members are zero-based, you can use the following version:

public static Array CreateInstance(Type elementType, int length);

The first argument is used to specify the type of array you want to create. You are allowed to create an array of any type, that is, an array of primitive values or an array of objects. The first argument is declared as Type. This means that it can be anything. For this reason, you can use the typeof operator to cast your type. Therefore, pass the type or the class in the parentheses of the typeof operator.

The second argument specifies the number of members of the array. Using the Array class, you can create an array as follows:

Array numbers = Array.CreateInstance(typeof(double), length);

You can also use the var or the dynamic keyword to declare the variable. Here is an example:

var numbers = Array.CreateInstance(typeof(double), 5);

ApplicationPractical Learning: Creating an Array

The Length of an Array

We know that if you declare a variable for an array but don't initialize it, you must specify the number of elements of the array. Here is an example:

public class Exercise
{
    public static void Main()
    {
        double[] numbers = new double[5];
    }
}

If you use the Array class to create an array, you must pass this constant integer as the second argument of the CreateInstance() method from the the above version. Here is an example:

using System;

public class Exercise
{
    public static void Main()
    {
        var numbers = Array.CreateInstance(typeof(double), 5);
    }
}

If the array exists already, that is, if you have already created the array or you are using an array created by someone else, to find out the number of items it contains, you can access its Length property (we already know that the length of an array is the number of elements it contains).

As an alternative, you can call the Array.GetLength() method. Its syntax is:

public int GetLength(int dimension);

For a one-dimensional array, you must pass the argument as 0. This method returns an integer that represents the number of items in the array.

The Rank of an Array

We have seen that the square brackets are used to specify that you are declaring an array. If you are creating a one-dimensional array, we saw that you could type a number in the square bracket. If you are creating a two-dimensional array, you type two numbers separated by a comma in the second pair of square brackets. Each number, whether it is one, two, or more is a placeholder for what is referred to as a dimension. In other words, a one dimensional array has a dimension of one. A two-dimensional array has a dimension of 2, and so on.

To find out the dimension of an array, the Array class provides the Rank property. Therefore, to know the dimension of an existing array, you can access its Rank property.

Fundamental Operations on an Array

Adding a Value to an Array

We know that, to initialize an array, you can open the curly brackets and list its members separated by commas, or you could access each member and assign it the desired value. To support the ability to add members to an array, the Array class is equipped with a method named SetValue that comes in different versions. To add a new item to the types of arrays we have used so far, you can call the following version of the Array.SetValue() method:

public void SetValue(object value, int index);

The first argument is the value to add to the list. The second argument is the index of the member to be added. The first item has index 1; the second item has index 2, and so on. If the array is a list of primitive values, simply pass the value for the first argument. Here are examples of calling the method:

using System;

public class Exercise
{
    public static void Main()
    {
        Array numbers = Array.CreateInstance(typeof(double), 5);

        numbers.SetValue(7628.937, 0);
        numbers.SetValue(6.48, 1);
        numbers.SetValue(574.9, 2);
        numbers.SetValue(293749.064, 3);
        numbers.SetValue(0.70257, 4);
    }
}

If the array is a list of objects, use any technique to create an object and pass it as the first argument.

We indicated that whenever you create an array, you are in fact declaring an instance of the Array class. Therefore, even if you create an array using the square bracket formula, you can still call the SetValue() method to specify any member of the array. Here is an example:

public class Exercise
{
    public static void Main()
    {
        var numbers = new double[5];

        numbers.SetValue(7628.937, 0);
        numbers.SetValue(6.48, 1);
        numbers.SetValue(574.9, 2);
        numbers.SetValue(293749.064, 3);
        numbers.SetValue(0.70257, 4);
    }
}

The Array class provides a SetValue() version for each corresponding CreateInstance() method we reviewed earlier.

ApplicationPractical Learning: Adding Objects to an Array

Getting a Value from an Array

To support the ability to retrieve the value of a member of an array, the Array class is equipped with a method named GetValue that is overloaded with a version corresponding to each version of the CreateInstance() and the SetValue() methods. For example, to access the values stored in a one-dimensional array, you can call this version:

public object GetValue(int index);

The index argument is the zero-based index of the member whose value you want to access. If the array is a list of primitive values, the Array.GetValue() method directly produces the value stored in the indicated position. Here is an example:

using static System.Console;

public class Exercise
{
    public static void Main()
    {
        var numbers = new double[5];

        numbers.SetValue(7628.937, 0);
        numbers.SetValue(6.48, 1);
        numbers.SetValue(574.9, 2);
        numbers.SetValue(293749.064, 3);
        numbers.SetValue(0.70257, 4);

        WriteLine("Number: " + numbers.GetValue(0));
        WriteLine("=================================");
    }
}

This would produce:

Number: 7628.937
=================================
Press any key to continue . . .

When calling the Array.GetValue() method, if you pass an invalid value, the compiler would throw an IndexOutOfRangeException exception.

Notice that the Array.GetValue() returns an anonymous object. This means that it can return anything. Therefore, if the array you are using is a list of objects, you must cast the returned object to the appropriate class.

When calling the Array.GetValue() method, if you pass an invalid value, the webpage would throw an exception.

Practical LearningPractical Learning: Getting the Objects of an Arrray

Looping for an Array

To access one member of the array at a time, you can use a loop to access any member using its index. You can use any of the classic three loops: for, while, or do...while. Here is an example that uses a for loop and the Length property to know the number of members of an array:

using static System.Console;

public class Exercise
{
    public static void Main()
    {
        var numbers = new double[5];

        numbers.SetValue(7628.937, 0);
        numbers.SetValue(6.48, 1);
        numbers.SetValue(574.9, 2);
        numbers.SetValue(293749.064, 3);
        numbers.SetValue(0.70257, 4);

        for (int i = 0; i < numbers.Length; i++)
            WriteLine("Number: " + numbers.GetValue(i));
        WriteLine("=================================");
    }
}

This would produce:

Number: 7628.937
Number: 6.48
Number: 574.9
Number: 293749.064
Number: 0.70257
=================================
Press any key to continue . . .

Practical LearningPractical Learning: Looping Through an Arrray of Objects

  1. In the Solution Explorer, right-click Program.cs and click Rename
  2. Type CountriesStatistics to get CountriesStatistics.cs
  3. Read the message box and click Yes
  4. In the Solution Explorer, double-click CountriesStatistics.cs to access it
  5. To display the list of states, change the document as follows: 
    using System;

namespace CountriesStatistics2
{
    public class CountriesStatistics
    {
        public static void Main(string[] args)
        {
            Array states = Array.CreateInstance(typeof(Federation), 30);
            Array regions = Array.CreateInstance(typeof(Region), 9);

            regions.SetValue(new Region() { Designation = "East North Central", Description = "The East North Central region includes the states around the Great Lakes." }, 0);
            regions.SetValue(new Region() { Designation = "East South Central", Description = "The East South Central portion is one of the regions designated as the South." }, 1);
            regions.SetValue(new Region() { Designation = "New England", Description = "New England is the group of states in the North-East region. It is delimited in the North and North-East by Canada, in the East by the Atlantic Ocean, and in the South and West by the New York state." }, 2);
            regions.SetValue(new Region() { Designation = "Mid-Atlantic", Description = "Mid-Atlantic is a region situated in the south of New England. Mid-Atlantic is one of the regions defined by the Census bureau for statistical purposes." }, 3);
            regions.SetValue(new Region() { Designation = "Mountain", Description = "Like the name suggests, the Mountain region covers states known for their mountaneous characteristics. They are also covered by desertic areas." }, 4);
            regions.SetValue(new Region() { Designation = "Pacific", Description = "The Pacific region covers the costal western states plus the two non-continental states of Alaska and the Hawaiian islands. All states in this region have a coast on the Pacific Ocean." }, 5);
            regions.SetValue(new Region() { Designation = "South Atlantic", Description = "The South Atlantic region includes the states in the South-East part but also counts the Disctrict of Columbia." }, 6);
            regions.SetValue(new Region() { Designation = "West North Central", Description = "The West North Central region includes the states in the Great Planes area. This reqion is divided from the East North Central part by the Mississippi River. This region is characterized by vast agricultural farms and high employment." }, 7);
            regions.SetValue(new Region() { Designation = "West South Central", Description = "The West South Central part is one of the regions with (only) four states. The imposing Texas state is both the largest and the most populous state in the region." }, 8);

            states.SetValue(new Federation() { Abbreviation = "RI", Name = "Rhode Island  ", Area =   1545, AreaSqrKms =    4002, AdmissionUnionDate = "05/29/1790", AdmissionUnionOrder = 13, Capital = "Providence    ", Region = (Region)(regions.GetValue(2)) }, 0);
            states.SetValue(new Federation() { Abbreviation = "OH", Name = "Ohio          ", Area =  44828, AreaSqrKms =  116103, AdmissionUnionDate = "03/01/1803", AdmissionUnionOrder = 17, Capital = "Columbus      ", Region = (Region)(regions.GetValue(0)) }, 1);
            states.SetValue(new Federation() { Abbreviation = "KY", Name = "Kentucky      ", Area =  40411, AreaSqrKms =  104665, AdmissionUnionDate = "06/01/1792", AdmissionUnionOrder = 15, Capital = "Frankfort     ", Region = (Region)(regions.GetValue(1)) }, 2);
            states.SetValue(new Federation() { Abbreviation = "IA", Name = "Iowa          ", Area =  56276, AreaSqrKms =  145754, AdmissionUnionDate = "12/28/1846", AdmissionUnionOrder = 29, Capital = "Des Moines    ", Region = (Region)(regions.GetValue(7)) }, 3);
            states.SetValue(new Federation() { Abbreviation = "WI", Name = "Wisconsin     ", Area =  65503, AreaSqrKms =  169653, AdmissionUnionDate = "05/29/1848", AdmissionUnionOrder = 30, Capital = "Madison       ", Region = (Region)(regions.GetValue(0)) }, 4);
            states.SetValue(new Federation() { Abbreviation = "VT", Name = "Vermont       ", Area =   9615, AreaSqrKms =   24903, AdmissionUnionDate = "03/04/1791", AdmissionUnionOrder = 14, Capital = "Montpelier    ", Region = (Region)(regions.GetValue(2)) }, 5);
            states.SetValue(new Federation() { Abbreviation = "ID", Name = "Idaho         ", Area =  83574, AreaSqrKms =  216456, AdmissionUnionDate = "07/03/1890", AdmissionUnionOrder = 43, Capital = "Boise         ", Region = (Region)(regions.GetValue(4)) }, 6);
            states.SetValue(new Federation() { Abbreviation = "ME", Name = "Maine         ", Area =  35387, AreaSqrKms =   91653, AdmissionUnionDate = "03/15/1820", AdmissionUnionOrder = 23, Capital = "Augusta       ", Region = (Region)(regions.GetValue(2)) }, 7);
            states.SetValue(new Federation() { Abbreviation = "OR", Name = "Oregon        ", Area =  98386, AreaSqrKms =  254819, AdmissionUnionDate = "02/14/1859", AdmissionUnionOrder = 33, Capital = "Salem         ", Region = (Region)(regions.GetValue(5)) }, 8);
            states.SetValue(new Federation() { Abbreviation = "ND", Name = "North Dakota  ", Area =  70704, AreaSqrKms =  183123, AdmissionUnionDate = "11/02/1889", AdmissionUnionOrder = 39, Capital = "Bismarck      ", Region = (Region)(regions.GetValue(7)) }, 9);
            states.SetValue(new Federation() { Abbreviation = "IN", Name = "Indiana       ", Area =  36420, AreaSqrKms =   94328, AdmissionUnionDate = "12/11/1816", AdmissionUnionOrder = 19, Capital = "Indianapolis  ", Region = (Region)(regions.GetValue(0)) }, 10);
            states.SetValue(new Federation() { Abbreviation = "MS", Name = "Mississippi   ", Area =  48434, AreaSqrKms =  125443, AdmissionUnionDate = "12/10/1817", AdmissionUnionOrder = 20, Capital = "Jackson       ", Region = (Region)(regions.GetValue(1)) }, 11);
            states.SetValue(new Federation() { Abbreviation = "TX", Name = "Texas         ", Area = 268601, AreaSqrKms =  695676, AdmissionUnionDate = "12/29/1845", AdmissionUnionOrder = 28, Capital = "Austin        ", Region = (Region)(regions.GetValue(8)) }, 12);
            states.SetValue(new Federation() { Abbreviation = "MT", Name = "Montana       ", Area = 147046, AreaSqrKms =  380850, AdmissionUnionDate = "11/08/1889", AdmissionUnionOrder = 41, Capital = "Helena        ", Region = (Region)(regions.GetValue(4)) }, 13);
            states.SetValue(new Federation() { Abbreviation = "NC", Name = "North Carolina", Area =  53821, AreaSqrKms =  139397, AdmissionUnionDate = "11/21/1789", AdmissionUnionOrder = 12, Capital = "Raleigh       ", Region = (Region)(regions.GetValue(6)) }, 14);
            states.SetValue(new Federation() { Abbreviation = "TN", Name = "Tennessee     ", Area =  42146, AreaSqrKms =  109158, AdmissionUnionDate = "06/01/1796", AdmissionUnionOrder = 16, Capital = "Nashville     ", Region = (Region)(regions.GetValue(1)) }, 15);
            states.SetValue(new Federation() { Abbreviation = "NE", Name = "Nebraska      ", Area =  77358, AreaSqrKms =  200358, AdmissionUnionDate = "03/01/1867", AdmissionUnionOrder = 37, Capital = "Lincoln       ", Region = (Region)(regions.GetValue(7)) }, 16);
            states.SetValue(new Federation() { Abbreviation = "IL", Name = "Illinois      ", Area =  57918, AreaSqrKms =  150007, AdmissionUnionDate = "12/03/1818", AdmissionUnionOrder = 21, Capital = "Springfield   ", Region = (Region)(regions.GetValue(0)) }, 17);
            states.SetValue(new Federation() { Abbreviation = "KS", Name = "Kansas        ", Area =  82282, AreaSqrKms =  213110, AdmissionUnionDate = "01/29/1861", AdmissionUnionOrder = 34, Capital = "Topeka        ", Region = (Region)(regions.GetValue(7)) }, 18);
            states.SetValue(new Federation() { Abbreviation = "NH", Name = "New Hampshire ", Area =   9351, AreaSqrKms =   24219, AdmissionUnionDate = "06/21/1788", AdmissionUnionOrder =  9, Capital = "Concord       ", Region = (Region)(regions.GetValue(2)) }, 19);
            states.SetValue(new Federation() { Abbreviation = "DE", Name = "Delaware      ", Area =   2489, AreaSqrKms =    6447, AdmissionUnionDate = "12/07/1787", AdmissionUnionOrder =  1, Capital = "Dover         ", Region = (Region)(regions.GetValue(6)) }, 20);
            states.SetValue(new Federation() { Abbreviation = "NJ", Name = "New Jersey    ", Area =   8722, AreaSqrKms =   22590, AdmissionUnionDate = "12/18/1787", AdmissionUnionOrder =  3, Capital = "Trenton       ", Region = (Region)(regions.GetValue(3)) }, 21);
            states.SetValue(new Federation() { Abbreviation = "AK", Name = "Alaska        ", Area = 656424, AreaSqrKms = 1700139, AdmissionUnionDate = "01/03/1959", AdmissionUnionOrder = 49, Capital = "Juneau        ", Region = (Region)(regions.GetValue(5)) }, 22);
            states.SetValue(new Federation() { Abbreviation = "NM", Name = "New Mexico    ", Area = 121598, AreaSqrKms =  314939, AdmissionUnionDate = "01/06/1912", AdmissionUnionOrder = 47, Capital = "Santa Fe      ", Region = (Region)(regions.GetValue(4)) }, 23);
            states.SetValue(new Federation() { Abbreviation = "NY", Name = "New York      ", Area =  54475, AreaSqrKms =  141089, AdmissionUnionDate = "07/26/1788", AdmissionUnionOrder = 11, Capital = "Albany        ", Region = (Region)(regions.GetValue(3)) }, 24);
            states.SetValue(new Federation() { Abbreviation = "CA", Name = "California    ", Area = 163707, AreaSqrKms =  424002, AdmissionUnionDate = "09/09/1850", AdmissionUnionOrder = 31, Capital = "Sacramento    ", Region = (Region)(regions.GetValue(5)) }, 25);
            states.SetValue(new Federation() { Abbreviation = "MO", Name = "Missouri      ", Area =  69709, AreaSqrKms =  180546, AdmissionUnionDate = "08/10/1821", AdmissionUnionOrder = 24, Capital = "Jefferson City", Region = (Region)(regions.GetValue(7)) }, 26);
            states.SetValue(new Federation() { Abbreviation = "OK", Name = "Oklahoma      ", Area =  69903, AreaSqrKms =  181049, AdmissionUnionDate = "11/16/1907", AdmissionUnionOrder = 46, Capital = "Oklahoma City ", Region = (Region)(regions.GetValue(8)) }, 27);
            states.SetValue(new Federation() { Abbreviation = "PA", Name = "Pennsylvania  ", Area =  46058, AreaSqrKms =  119291, AdmissionUnionDate = "12/12/1787", AdmissionUnionOrder =  2, Capital = "Harrisburg    ", Region = (Region)(regions.GetValue(3)) }, 28);
            states.SetValue(new Federation() { Abbreviation = "SC", Name = "South Carolina", Area =  32007, AreaSqrKms =   82898, AdmissionUnionDate = "05/23/1788", AdmissionUnionOrder =  8, Capital = "Columbia      ", Region = (Region)(regions.GetValue(6)) }, 29);

            Console.WriteLine("                                 Area      Admission to Union");
            Console.WriteLine(" # Abbrv State Name        SqrMls     Km2    Date        Order  Capital         Region");
            Console.WriteLine("----------------------------------------------------------------------------------------------------");

            for (int counter = 0; counter <= states.Length - 1; counter++)
            {
                Federation stt = (Federation)states.GetValue(counter);

                Console.WriteLine("{0,2}  {1,2}   {2}   {3,6}   {4,7}   {5,8} {6,5}   {7}  {8}",
                                  counter + 1, stt.Abbreviation, stt.StateName,
                                  stt.AreaSqrMiles, stt.AreaSqrKms, stt.AdmissionUnionDate,
                                  stt.AdmissionUnionOrder, stt.Capital, stt.Region.Designation);
            }
            Console.WriteLine("====================================================================================================");
        }
    }
}
  6. To execute, on the main menu, click Debug -> Start Without Debugging: 
                                     Area      Admission to Union
 # Abbrv State Name        SqrMls     Km2    Date        Order  Capital         Region
----------------------------------------------------------------------------------------------------
 1  RI   Rhode Island       1545      4002   05/29/1790    13   Providence      New England
 2  OH   Ohio              44828    116103   03/01/1803    17   Columbus        East North Central
 3  KY   Kentucky          40411    104665   06/01/1792    15   Frankfort       East South Central
 4  IA   Iowa              56276    145754   12/28/1846    29   Des Moines      West North Central
 5  WI   Wisconsin         65503    169653   05/29/1848    30   Madison         East North Central
 6  VT   Vermont            9615     24903   03/04/1791    14   Montpelier      New England
 7  ID   Idaho             83574    216456   07/03/1890    43   Boise           Mountain
 8  ME   Maine             35387     91653   03/15/1820    23   Augusta         New England
 9  OR   Oregon            98386    254819   02/14/1859    33   Salem           Pacific
10  ND   North Dakota      70704    183123   11/02/1889    39   Bismarck        West North Central
11  IN   Indiana           36420     94328   12/11/1816    19   Indianapolis    East North Central
12  MS   Mississippi       48434    125443   12/10/1817    20   Jackson         East South Central
13  TX   Texas            268601    695676   12/29/1845    28   Austin          West South Central
14  MT   Montana          147046    380850   11/08/1889    41   Helena          Mountain
15  NC   North Carolina    53821    139397   11/21/1789    12   Raleigh         South Atlantic
16  TN   Tennessee         42146    109158   06/01/1796    16   Nashville       East South Central
17  NE   Nebraska          77358    200358   03/01/1867    37   Lincoln         West North Central
18  IL   Illinois          57918    150007   12/03/1818    21   Springfield     East North Central
19  KS   Kansas            82282    213110   01/29/1861    34   Topeka          West North Central
20  NH   New Hampshire      9351     24219   06/21/1788     9   Concord         New England
21  DE   Delaware           2489      6447   12/07/1787     1   Dover           South Atlantic
22  NJ   New Jersey         8722     22590   12/18/1787     3   Trenton         Mid-Atlantic
23  AK   Alaska           656424   1700139   01/03/1959    49   Juneau          Pacific
24  NM   New Mexico       121598    314939   01/06/1912    47   Santa Fe        Mountain
25  NY   New York          54475    141089   07/26/1788    11   Albany          Mid-Atlantic
26  CA   California       163707    424002   09/09/1850    31   Sacramento      Pacific
27  MO   Missouri          69709    180546   08/10/1821    24   Jefferson City  West North Central
28  OK   Oklahoma          69903    181049   11/16/1907    46   Oklahoma City   West South Central
29  PA   Pennsylvania      46058    119291   12/12/1787     2   Harrisburg      Mid-Atlantic
30  SC   South Carolina    32007     82898   05/23/1788     8   Columbia        South Atlantic
====================================================================================================
Press any key to continue . . .
  7. Press Enter to close the window and return to your programming environment
  8. Close your programming environment
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