Description: The following example shows the usage of Regular Expressions in C#. The program basically has all the Validation Programs using Regular Expression. /* csc /r:System.Text.RegularExpressions.dll,System.dll Validation.cs */ using System.Text.RegularExpressions; using System; class Validation { public static void Main() { string strToTest; Validation objValidate=new Validation(); Console.Write("Enter a String to Test for Alphabets:"); strToTest=Console.ReadLine(); //Change here...