using System;  

using System.Collections.Generic;  

using System.ComponentModel;  

using System.Data;  

using System.Drawing;  

using System.Text;  

using System.Windows.Forms;  

namespace CalculatorApp  

{  

    public partial class Form1 : Form  

    {  

        double FirstNumber;  

        string Operation;  

        public Form1()  

        {  

            InitializeComponent();  

        }  

        private void n1_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "1";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "1";  

            }  

        }  

        private void n2_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "2";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "2";  

            }  

        }  

        private void n3_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "3";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "3";  

            }  

        }  

        private void n4_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "4";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "4";  

            }  

        }  

        private void n5_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "5";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "5";  

            }  

        }  

        private void n6_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "6";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "6";  

            }  

        }  

        private void n7_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "7";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "7";  

            }  

        }  

        private void n8_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "0" && textBox1.Text != null)  

            {  

                textBox1.Text = "8";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "8";  

            }  

        }  

        private void n9_Click(object sender, EventArgs e)  

        {  

            if (textBox1.Text == "" && textBox1.Text != null)  

            {  

                textBox1.Text = "9";  

            }  

            else  

            {  

                textBox1.Text = textBox1.Text + "9";  

            }  

        }  

        private void n0_Click(object sender, EventArgs e)  

        {  

            textBox1.Text = textBox1.Text + "0";  

        }  

        private void bad_Click(object sender, EventArgs e)  

        {  

            FirstNumber = Convert.ToDouble(textBox1.Text);  

            textBox1.Text = "0";  

            Operation = "+";  

        }  

        private void bsub_Click(object sender, EventArgs e)  

        {  

            FirstNumber = Convert.ToDouble(textBox1.Text);  

            textBox1.Text = "0";  

            Operation = "-";  

        }  

        private void bmul_Click(object sender, EventArgs e)  

        {  

            FirstNumber = Convert.ToDouble(textBox1.Text);  

            textBox1.Text = "0";  

            Operation = "*";  

        }  

        private void bdiv_Click(object sender, EventArgs e)  

        {  

            FirstNumber = Convert.ToDouble(textBox1.Text);  

            textBox1.Text = "0";  

            Operation = "/";  

        }  

        private void bc_Click(object sender, EventArgs e)  

        {  

            textBox1.Text = "0";  

        }  

        private void ndot_Click(object sender, EventArgs e)  

        {  

            textBox1.Text = textBox1.Text + ".";  

        }  

        private void nequal_Click(object sender, EventArgs e)  

        {  

            double SecondNumber;  

            double Result;  

            SecondNumber = Convert.ToDouble(textBox1.Text);  

            if (Operation == "+")  

            {  

                Result = (FirstNumber + SecondNumber);  

                textBox1.Text = Convert.ToString(Result);  

                FirstNumber = Result;  

            }  

            if (Operation == "-")  

            {  

                Result = (FirstNumber - SecondNumber);  

                textBox1.Text = Convert.ToString(Result);  

                FirstNumber = Result;  

            }  

            if (Operation == "*")  

            {  

                Result = (FirstNumber * SecondNumber);  

                textBox1.Text = Convert.ToString(Result);  

                FirstNumber = Result;  

            }  

            if (Operation == "/")  

            {  

                if (SecondNumber == 0)  

                {  

                    textBox1.Text = "Cannot divide by zero";  

                }  

                else  

                {  

                    Result = (FirstNumber / SecondNumber);  

                    textBox1.Text = Convert.ToString(Result);  

                    FirstNumber = Result;  

                }  

            }  

        }  

    }  

}