How to display the elemens of arraylist in C#

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Hi,
I have written the following code:

using System;
using System.Collections;

namespace ArrayList1
{
    class Program
    {
        ArrayList a1 = new ArrayList();

        static void Main(string[] args)
        {
            Program objProg = new Program();
            objProg.a1.Add(10);
            objProg.a1.Add(5.67);
            objProg.a1.Add("abcde");
            objProg.a1.Add('c');
            foreach(int i in objProg.a1)
            Console.WriteLine("i");
        }
    }
}

I am getting run-time exception. Some body please guide me.

Zulfi.

What I have tried:

I did web search but still code not working.

Posted 1-Jun-19 14:16pm

zak100

Updated 27-Mar-20 7:35am

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phil.o · Answer 1 · 2019-06-01T17:45:00

Try:

C#

class Program
{
   static ArrayList a1 = new ArrayList();

   static void Main(string[] args)
   {
      a1.Add(10);
      a1.Add(5.67);
      a1.Add("abcde");
      a1.Add('c');
      foreach (object i in a1)
      {
         Console.WriteLine(i);
      }
   }
}

Key points:
- Creating a new instance of the program class in the Main method to be able to access a class member is not a good practice.
- a1 class variable has to be static to be accessed from a static method.
- In the foreach loop, you cannot declare i as an int since your arraylist does not hold only integer values. The common type which can match an integer, a double, a string and a character is an object.
- Console.WriteLine("i"); will print the letter i instead of the value of the variable i.

BillWoodruff · Answer 2 · 2019-06-03T03:42:00

The ArrayList is an old feature, and is deprecated [^] now because it is a very expensive (memory, time to access) way to create a collection of objects of mixed Types, and using it, errors will not occur at compile-time.

Its use is also ... in almost all cases ... a violation of good OOP/SOLID principles: in good practice all these bits of data you are putting into the ArrayList mean something. Use a Class (or Struct) to store your data:

C#

public class Data
{
   public int Number10 { set; get; }

   // ...
}

Or, if you must have a structure where you can add multiple Types at run-time, later versions of C# provide the 'ExpandoObject [^] in the System.Dynamic NameSpace (and, the more complex 'DynamicObject):

C#

dynamic person = new ExpandoObject();
person.Name = "John";
person.Surname = "Doe";
person.Age = 42;

// access by Key
int age = person.Age;

foreach (var kvp in person)
{
    Console.WriteLine($"{kvp.ToString()}");
}

// output in Console Window:
[Name, John]
[Surname, Doe]
[Age, 42]

How to display the elemens of arraylist in C#

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