Retirement Years Calculator In C#

Write a Program that asks the user for her birthday. If the user entered a valid date (check to make sure and
keep asking if the user did not enter a date), display a message box telling the user how many years until she
reaches the retirement age of 65. If the user is older than 65, congratulate her on a long life!

Program:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Globalization;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace Question4

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            DateTime D;

            string CombinedDate = String.Format("{0}-{1}-{2}", textBox1.Text, textBox2.Text, textBox3.Text);

            if (DateTime.TryParseExact(CombinedDate, "d-M-yyyy", DateTimeFormatInfo.InvariantInfo, DateTimeStyles.None, out D))

            {

                int age = Convert.ToInt32(textBox3.Text);

                age = 2015 - age;

                MessageBox.Show("Your Age Is " + age);

                if (age >= 65)

                {

                    MessageBox.Show("We Congratulate you on your long life");

                }

                else

                {

                    age = (-age) + 65; 

                    MessageBox.Show("You Have Got "+age+" Years For Your Retirement");

                }

            }

            else

            {

                MessageBox.Show("invalid Date Entered");

            }

        }

    }

}