C# Program of calculator(mobile 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 calc

{   

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();           

        }

       Double temp=0;           // global declaration     

      

        // addition performed

        private void button1_Click(object sender, EventArgs e)

        {          

            Double d1;

            if(label4.Text=="=")

            {

                label1.Text ="+";

                label2.Text = label3.Text;

                label3.Text = "";

                label4.Text = "";

                textBox1.Clear();

            }

            else if (label1.Text == "-")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp - d1;

                label1.Text = "+";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if(label1.Text == "*")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp * d1;

                label1.Text = "+";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if(label1.Text == "/")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp / d1;

                label1.Text = "+";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else

            {

                d1 = Convert.ToDouble(textBox1.Text);

                label1.Text = "+";

                temp = temp + d1;

                textBox1.Clear();

                label2.Text = Convert.ToString(temp);

            }             

        }

        //subtraction

        private void button2_Click(object sender, EventArgs e)

        {            

            Double d1;

            if (label4.Text == "=")

            {

                label1.Text = "-";

                label2.Text = label3.Text;

                label3.Text = "";

                label4.Text = "";

                textBox1.Clear();

            }

            else if (label1.Text == "+")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp + d1;

                label1.Text = "-";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if(label1.Text == "*")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp * d1;

                label1.Text = "-";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if (label1.Text == "/")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp / d1;

                label1.Text = "-";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else

            {

                d1 = Convert.ToDouble(textBox1.Text);

                label1.Text = "-";

                temp = temp - d1;

                textBox1.Clear();

                label2.Text = Convert.ToString(temp);

            }

        }

        //multiplication

        private void button3_Click(object sender, EventArgs e)

        {

            Double d1;

            if (label4.Text == "=")

            {

                label1.Text = "*";

                label2.Text = label3.Text;

                label3.Text = "";

                label4.Text = "";

                textBox1.Clear();

            }

            else if (label1.Text == "+")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp + d1;

                label1.Text = "*";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if (label1.Text == "-")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp - d1;

                label1.Text = "*";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if (label1.Text == "/")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp / d1;

                label1.Text = "*";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else

            {

                d1 = Convert.ToDouble(textBox1.Text);

                label1.Text = "*";

                textBox1.Clear();

                temp = temp * d1;

                label2.Text = Convert.ToString(temp);

            }

        }

        //division

        private void button4_Click(object sender, EventArgs e)

        {

            Double d1;

            if (label4.Text == "=")

            {

                label1.Text = "/";

                label2.Text = label3.Text;

                label3.Text = "";

                label4.Text = "";

                textBox1.Clear();

            }

            else if (label1.Text == "+")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp + d1;

                label1.Text = "/";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if (label1.Text == "-")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp - d1;

                label1.Text = "/";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else if (label1.Text == "*")

            {

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp * d1;

                label1.Text = "/";

                label2.Text = Convert.ToString(temp);

                textBox1.Clear();

            }

            else

            {

                d1 = Convert.ToDouble(textBox1.Text);

                label1.Text = "/";

                textBox1.Clear();

                temp = temp / d1;

                label2.Text = Convert.ToString(temp);

            }

        }

        // equals button

        private void button6_Click(object sender, EventArgs e)

        {           

            if ((label1.Text=="+") && (label4.Text!="="))

            {

                Double d1;

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp + d1;

                label4.Text = "=";

                label3.Text = Convert.ToString(temp);

            }

            else if ((label1.Text == "-") && (label4.Text != "="))

            {

                Double d1;

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp - d1;

                label4.Text = "=";

                label3.Text = Convert.ToString(temp);

            }

            else if ((label1.Text == "*") && (label4.Text != "="))

            {

                Double d1;

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp * d1;

                label4.Text = "=";

                label3.Text = Convert.ToString(temp);

            }

            else if ((label1.Text == "/") && (label4.Text != "="))

            {

                Double d1;

                d1 = Convert.ToDouble(textBox1.Text);

                temp = temp / d1;

                label4.Text = "=";

                label3.Text = Convert.ToString(temp);      

            }

            else if (label1.Text == "")

            {

               //stop to calculate again and again

            }                     

        }

        //clear

        private void button5_Click(object sender, EventArgs e)

        {

            temp = 0;

            textBox1.Clear();

            label1.Text ="";

            label2.Text = "";

            label3.Text = "";

            label4.Text = "";

        }

        //for taking input only numbers and dot.

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)

        {

            if (!((e.KeyChar >= 48 && e.KeyChar <= 57) || e.KeyChar == 46 || e.KeyChar == 8 || e.KeyChar == 9))

                e.Handled = true;

        }

    }

}

                                                              Output