[Age calculator C#] how do I implement leap year control?

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C#

Visual-Studio

Hi,

A brief summary: I am very new to C# and this is my first time programming in this language. I have more experience with scripting languages. For a college assignment we must make an age calculator which calculates the age in days of the user, based on combo box input.

My question is, how (and where) do I implement leap year control within my code? I am aware of DateTime.IsLeapYear, however I am very unfamiliar with the syntax and do not know where to start with it.

I have added my code below so you can see my progress so far. I am working in Visual Studio 2017.

P.S. I must also implement a try/catch block somewhere, but as I said above I do not know where to start with it. Where would this go?

What I have tried:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace NumberOfDaysOld
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //=========================================================
            // DISPLAYS MONTHS OF THE YEAR IN THE MONTH COMBOBOX
            //=========================================================
            string[] monthArray = new string[12];
            monthArray[0] = "January";
            monthArray[1] = "February";
            monthArray[2] = "March";
            monthArray[3] = "April";
            monthArray[4] = "May";
            monthArray[5] = "June";
            monthArray[6] = "July";
            monthArray[7] = "August";
            monthArray[8] = "September";
            monthArray[9] = "October";
            monthArray[10] = "November";
            monthArray[11] = "December";

            for (int index = 0; index < monthArray.Length; index++)
            {
                comboBoxMonth.Items.Add(monthArray[index]);
            }

            //=========================================================
            // DISPLAYS YEARS 1900 TO CURRENT YEAR IN THE YEAR COMBOBOX
            //=========================================================

            for (int i = 1900; i <= DateTime.Now.Year; i++)
            {
                comboBoxYear.Items.Add(i.ToString());
            }

            //=========================================================
            // DISPLAYS DATES OF THE MONTH IN THE DAYS COMBOBOX
            //=========================================================

            for (int i = 1; i <= 31; i++)
            {
                comboBoxDay.Items.Add(i.ToString());
            }

        }

        private void timerDateTime_Tick(object sender, EventArgs e)
        {
            //=========================================================
            // DISPLAYS THE DATE AND TIME IN REALTIME
            //=========================================================

            labelDate.Text = DateTime.Now.ToShortDateString();
            labelTime.Text = DateTime.Now.ToLongTimeString();
        }

        private void comboBoxDay_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void comboBoxMonth_SelectedIndexChanged(object sender, EventArgs e)
        {

        }


        private void buttonCalculate_Click(object sender, EventArgs e)
        {
            DateTime dob = new DateTime(Convert.ToInt32(comboBoxYear.SelectedItem), comboBoxMonth.SelectedIndex + 1, Convert.ToInt32(comboBoxDay.SelectedItem));
            TimeSpan diff = DateTime.Now - dob;
            int days = (int)diff.TotalDays;
            MessageBox.Show(textBoxForename.Text + " is days old " + days.ToString());
        }

        }
    }
}