Arrays: An array is a group of like-typed variables that are referred to by a common name. 

Example:

// C# program to demonstrate the Arrays
using System;
 
class TECH {
 
    // Main Method
    public static void Main(string[] args)
    {
 
        // creating array
        int[] arr = new int[4];
 
        // initializing array
        arr[0] = 47;
        arr[1] = 77;
        arr[2] = 87;
        arr[3] = 97;
 
        // traversing array
        for (int i = 0; i < arr.Length; i++) {
 
            Console.WriteLine(arr[i]);
        }
    }
}

Output:

47
77
87
97

ArrayList: ArrayList represents an ordered collection of an object that can be indexed individually. It is basically an alternative to an array. It also allows dynamic memory allocation, adding, searching and sorting items in the list. 

Example:

// C# program to illustrate the ArrayList
using System;
using System.Collections;
 
class TECH {
 
    // Main Method
    public static void Main(string[] args)
    {
 
        // Create a list of strings
        ArrayList al = new ArrayList();
        al.Add("Atchu");
        al.Add("Atshaya");
        al.Add(10);
        al.Add(10.10);
 
        // Iterate list element using foreach loop
        foreach(var names in al)
        {
            Console.WriteLine(names);
        }
    }
}

Output:

Atchu
Atshaya
10
10.1

Difference Between Array and ArrayList