The Program in C# Program to display Sum of Series[9+99+999 + 9999…] is given below:

using System;

namespace SumOfSeries
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello Codeauri Family, enter the number of terms in the series:");
            int n = int.Parse(Console.ReadLine());

            int sum = 0;

            for (int i = 1; i <= n; i++)
            {
                int term = int.Parse("9" + new string('9', i));
                sum += term;
            }

            Console.WriteLine("Okay, the sum of the series is: " + sum);
            Console.ReadLine();
        }
    }
}

Output:

Hello Codeauri Family, enter the number of terms in the series:
8
Okay, the sum of the series is: 1111111092

Pro-Tips💡

Here are the step by step execution of above program:

1. The program starts by importing the System namespace, which provides access to various classes and methods, including the Console class.
2. The program then declares a namespace SumOfSeries and a class Program within it.
3. The Main method is the entry point of the program and it contains the logic to display the sum of the series [9 + 99 + 999 + 9999 …].
4. The program starts by displaying a message asking the user to enter the number of terms in the series.
5. The user input is read and parsed into an int variable n.
6. The sum variable is declared and initialized to 0. This variable will store the sum of the series.
7. The program then enters a for loop that will run n times. In each iteration of the loop, a new term of the series is calculated using int.Parse("9" + new string('9', i)), where i is the loop variable. The new string('9', i) creates a string of i number of 9s, which is concatenated with 9 to create the desired term.
8. The calculated term is then added to the sum variable.
9. After the loop is finished, the program displays the final sum of the series using Console.WriteLine.
10. Finally, the program waits for the user to press the Enter key before ending.