c#.txt

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

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

        float num1 = 0, num2 = 0;
        int oprClickCount = 0;
        bool isOprClick = false, isEqualClick = false;
        string opr;

        private void csharp_calculator_Load(object sender, EventArgs e)
        {
            // add button click event to all buttons
            foreach(Control c in Controls)
            {
                if(c is Button)
                {
                    if(c.Text != "Reset")
                    c.Click += new System.EventHandler(btn_click);
                }
            }
        }

       // create button click event

        public void btn_click(object sender, EventArgs e)
        {
            Button button = (Button)sender;

            if (!isOperator(button))// if the button is a number
            {
                if(isOprClick)
                {
                    num1 = float.Parse(textBox1.Text);
                    textBox1.Text = "";
                }
                // if the textbox text not contain "."
                if (!textBox1.Text.Contains("."))
                {
                    if (textBox1.Text.Equals("0") && !button.Text.Equals("."))
                    {
                        // delete the first "0"
                        // set button text to the textbox
                        // if the button text is not "."
                        textBox1.Text = button.Text;
                        isOprClick = false;
                    }
                    else
                    {
                        textBox1.Text += button.Text;
                        isOprClick = false;
                    }
                }

                else if (!button.Text.Equals("."))
                {
                    textBox1.Text += button.Text;
                    isOprClick = false;
                }
            }
            else // if the button is an operator [+ - / * =]
            {
                if(oprClickCount == 0)// if it's the first time we click on an operator
                {
                    oprClickCount++;
                    // convert textbox text to float and set it into num1
                    num1 = float.Parse(textBox1.Text);
                    // get the operator from button text
                    opr = button.Text;
                    // set oprclick to true
                    isOprClick = true;
                }
                else
                {
                    if(!button.Text.Equals("="))// if the operation is not "="
                    {
                        if(!isEqualClick)
                        {
                            num2 = float.Parse(textBox1.Text);
                            textBox1.Text = Convert.ToString(calc(opr, num1, num2));
                            num2 = float.Parse(textBox1.Text);
                            opr = button.Text;
                            isOprClick = true;
                            isEqualClick = false;
                        }else
                        {
                            isEqualClick = false;
                            opr = button.Text;
                        }
                    }
                    else
                    {
                        num2 = float.Parse(textBox1.Text);
                        textBox1.Text = Convert.ToString(calc(opr, num1, num2));
                        num1 = float.Parse(textBox1.Text);
                        isOprClick = true;
                        isEqualClick = true;
                    }
                }
            }

        }

        // create a function to check if the clicked button is a number(+ '.') or an operators
        public bool isOperator(Button button)
        {
            string buttonText = button.Text;

            if(buttonText.Equals("+") || buttonText.Equals("-") || 
                buttonText.Equals("X") || buttonText.Equals("/") ||
                buttonText.Equals("="))
            {
                return true;
            }
            else
            {
                return false;
            }

        }

        // function to calculate
        public float calc(string opr, float n1, float n2)
        {
            float result = 0;

            switch (opr)
            {
                case"+":
                    result = n1 + n2;
                    break;
                case "-":
                    result = n1 - n2;
                    break;
                case "X":
                    result = n1 * n2;
                    break;
                case "/":
                    if(n2 != 0)
                         result = n1 / n2;
                    break;
            }
            return result;
        }

        // button reset to make another calculation
        private void buttonReset_Click(object sender, EventArgs e)
        {
            num1 = 0;
            num2 = 0;
            opr = "";
            isOprClick = false;
            isEqualClick = false;
            oprClickCount = 0;
            textBox1.Text = "0";
        }
    }
}