Calculator

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;

namespace WindowsFormsApplication1

{

    public partial class calculator : Form

    {

        public calculator()

        {

            InitializeComponent();

        }

        string var1, var2, op;

        private void btn1_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text+((Button)sender).Text;

        }

        private void btn2_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text+((Button)sender).Text;

        }

        private void btn3_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn4_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn5_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn6_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn7_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn8_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn9_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btn0_Click(object sender, EventArgs e)

        {

            textBox1.Text = textBox1.Text + ((Button)sender).Text;

        }

        private void btnplus_Click(object sender, EventArgs e)

        {

            var1 = textBox1.Text;

            op = "+";

            textBox1.Text = "";

        }

        private void btnminus_Click(object sender, EventArgs e)

        {

            var1 = textBox1.Text;

            op = "-";

            textBox1.Text = "";

        }

        private void btnmul_Click(object sender, EventArgs e)

        {

            var1 = textBox1.Text;

            op = "*";

            textBox1.Text = "";

        }

        private void btndiv_Click(object sender, EventArgs e)

        {

            var1 = textBox1.Text;

            op = "/";

            textBox1.Text = "";

        }

        private void btnequal_Click(object sender, EventArgs e)

        {

            var2 = textBox1.Text;

            if (op == "+")

            {

                textBox1.Text = Convert.ToString(decimal.Parse(var1) + decimal.Parse(var2));

            }

            if (op == "-")

            {

                textBox1.Text = Convert.ToString(decimal.Parse(var1) - decimal.Parse(var2));

            }

            if (op == "*")

            {

                textBox1.Text = Convert.ToString(decimal.Parse(var1) * decimal.Parse(var2));

            }

            if (op == "/")

            {

                textBox1.Text = Convert.ToString(decimal.Parse(var1) / decimal.Parse(var2));

            }

        }

        private void btnac_Click(object sender, EventArgs e)

        {

            textBox1.Text = "";

            var1 = "0";

            var2 = "0";

        }

    }

}