access modifiers

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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            Class1 a = new Class1();
            int d =a.add(9, 5);

            MessageBox.Show(d.ToString());



        }

    }
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace mynamespace
{
    class Class1
    {
        int a;
        int b;
        int c;

        public Class1()
        {

        }
        public Class1(int a1, int b1, int c1)
        {
            a = a1;
            b = b1;
            c = c1;
        }
        public int add(int a , int b)
        {
            int c=a+b;
            return c;
        }
    }
}