Why Collections are Preferred why not Arrays?

Yes, Collections are preferred then arrays, why because we have few advantages.

 1. no need to bother about element adding,element deleation...ect
 2. no need to bother about memory allocation.
 3. a little bit of performance and iteration also
 
and we have Collections also Index based Collections and key/value pair collections.

Index based collections implements ----> IList interface
 Example: ArrayList
interface IList : ICollection, IEnumerable
{
         bool    IsFixedSize { get; };
         bool    IsReadOnly { get; };
         int       Add(object value);  
        
        object this[int index] { get; set; }
}
  we can access an element using index
like
            ArrayList arr = new ArrayList();
            arr.Add("abc");
            arr.Add("def");
            arr.Add("jhi");
            Console.WriteLine(arr[1]);-------> index based access

key/value based collections implements---->IDictionary interface.
Example : SortedList
interface IDictionary : ICollection, IEnumerable
{
             bool    IsFixedSize { get; };
             bool    IsReadOnly { get; };
             ICollection  Keys { get; }
             ICollection Values { get; }
            object this[object key] { get; set; }
            void Add(object key, object value);
}