frmAddProduct

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

namespace frmAddProduct
{

    public partial class frmAddProduct : Form
    {
        private string _ProductName;
        private string _Category;
        private string _MfgDate;
        private string _ExpDate;
        private string _Description;

        private int _Quantity;
        private double _SellPrice;

        BindingSource showProductList = new BindingSource();


        public string Product_Name(string name)
        {

            if (!Regex.IsMatch(name, @"^[a-zA-Z]+$"))
                //Exception here
                return name;
        }
        public int Quantity(string qty)
        {
            if (!Regex.IsMatch(qty, @"^[0-9]"))
                //Exception here
                return Convert.ToInt32(qty);
        }
        public double SellingPrice(string price)
        {
            if (!Regex.IsMatch(price.ToString(), @"^(\d*\.)?\d+$"))
                //Exception here
                return Convert.ToDouble(price);
        }


        public frmAddProduct()
        {
            InitializeComponent();
        }


        private void frmAddProduct_Load(object sender, EventArgs e)
        {
            string[] ListOfProductCategory = {"Beverages" , "Bread/Bakery",
            "Canned/Jarred Goods", "Dairy", "Frozen Goods", "Meat",
            "Personal Care", "Other"};

            foreach (string listofproductcategory in ListOfProductCategory)
            {
                cbCategory.Items.Add(listofproductcategory);
            }
        }

        private void btnAddProduct_Click(object sender, EventArgs e)
        {
            _ProductName = Product_Name(txtProductName.Text);
            _Category = cbCategory.Text;
            _MfgDate = dtPickerMfgDate.Value.ToString("yyyy-MM-dd");
            _ExpDate = dtPickerExpDate.Value.ToString("yyyy-MM-dd");
            _Description = richTxtDescription.Text;
            _Quantity = Quantity(txtQuantity.Text);
            _SellPrice = SellingPrice(txtSellPrice.Text);
            showProductList.Add(new ProductClass(_ProductName, _Category,
                _MfgDate, _ExpDate, _SellPrice, _Quantity, _Description));
            gridViewProductList.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
            gridViewProductList.DataSource = showProductList;
        }
       class NumberFormatException : Exception
        {
            public NumberFormatException (string qty) : base(qty) { }
        }
        class StringFormatException : Exception
        {
            public StringFormatException (string name) : base (name) { }
        }
        class CurrencyFormatException : Exception
        {
            public CurrencyFormatException (string price) : base (price) { }
        }

    }
}