What are key-based I/O collections in C#?

The key-based I/O Collections in C# is what we call a SortedList −

SortedList<TKey,TValue>

The SortedList class represents a collection of key-and-value pairs that are sorted by the keys and are accessible by key and by index. This is how both of them gets added in a SortedList −

s.Add("Sub1", "Physics");
s.Add("Sub2", "Chemistry");
s.Add("Sub3", "Biology");
s.Add("Sub4", "Java");

The following is an example displaying the keys and values in a SortedList −

Example

using System;
using System.Collections;

namespace Demo {
   class Program {
      static void Main(string[] args) {
         SortedList s = new SortedList();

         s.Add("Sub1", "Economics");
         s.Add("Sub2", "Accountancy");
         s.Add("Sub3", "Business Studies");
         s.Add("Sub4", "English");

         Console.WriteLine("Capacity = " + s.Capacity);

         // get a collection of the keys.
         ICollection key = s.Keys;

         foreach (string k in key) {
            Console.WriteLine(k + ": " + s[k]);
         }
      }
   }
}

Output

Capacity = 16
Sub1: Economics
Sub2: Accountancy
Sub3: Business Studies
Sub4: English