Write an application named EnterUppercaseLetters that asks the user to type an uppercase letter from the keyboard. If the character entered is an uppercase letter, display OK; if it is not an uppercase letter, display an error message. The program continues until the user types an exclamation point. C# C# C#

The solution code is given below

using System; using System.Linq;      public class Program { public static void Main() {  string[] letters = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T","U", "V", "W", "X", "Y", "Z"};    Console.WriteLine("Please input a letter: ");  string input_letter = Console.ReadLine();    if(letters.Contains(input_letter)){  Console.WriteLine("OK");  }else{  Console.WriteLine("Error. Not uppercase letter.");  }   } }

Explanation:

Firstly we import the necessary libraries, System and Linq (Line 1-2).

Next we create a string array to hold all uppercase letters (Line 8).

Next, we prompt user to input a letter using the ReadLine() method (Line 10 - 11)

At last, we define if and else conditions to check if the letters contains the input letter. If so, print ok else print an error message. (Line 13-17)