Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to implement all properties and events methods.

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System;
namespace InterfaceApplication
{
    public interface ITransactions
    {
        // interface members
        void ViewTransaction();
        double GetTransactionAmount();
    }
    public class Transaction : ITransactions
    {
        private string TransactionCode;
        private string TransactionDate;
        private double TransactionAmount;
        public Transaction()
        {
            TransactionCode = " ";
            TransactionDate = " ";
            TransactionAmount = 0.0;
        }
        public Transaction(string Code, string Date, double Amount)
        {
            TransactionCode = Code;
            TransactionDate = Date;
            TransactionAmount = Amount;
        }
        public double GetTransactionAmount()
        {
            return TransactionAmount;
        }
        public void ViewTransaction()
        {
            Console.WriteLine("TransactionCode: {0}", TransactionCode);
            Console.WriteLine("TransactionDate: {0}", TransactionDate);
            Console.WriteLine("TransactionAmount: {0}", GetTransactionAmount());
            Console.WriteLine();
        }
    }
    class Manager
    {
        static void Main(string[] args)
        {
            ITransactions t1 = new Transaction("001", "8/10/2012", 78900.00);
            ITransactions t2 = new Transaction("002", "9/10/2012", 451900.00);
            t1.ViewTransaction();
            t2.ViewTransaction();
            Console.ReadKey();
        }
    }
}