C# Simple Calculator

Form1.cs

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 SimpleCalculator 
{ 
    public partial class frmCalculator : Form 
    { 
        string operand1 = string.Empty; 
        string operand2 = string.Empty; 
        string result; 
        char operation; 
 
        public frmCalculator() 
        { 
            InitializeComponent(); 
        } 
 
        private void frmCalculator_Load(object sender, EventArgs e) 
        { 
            btnOne.Click += new EventHandler(btn_Click); 
            btnTwo.Click += new EventHandler(btn_Click); 
            btnThree.Click += new EventHandler(btn_Click); 
            btnFour.Click += new EventHandler(btn_Click); 
            btnFive.Click += new EventHandler(btn_Click); 
            btnSix.Click += new EventHandler(btn_Click); 
            btnSeven.Click += new EventHandler(btn_Click); 
            btnEight.Click += new EventHandler(btn_Click); 
            btnNine.Click += new EventHandler(btn_Click); 
            btnZero.Click += new EventHandler(btn_Click); 
            btnDot.Click += new EventHandler(btn_Click); 
        } 
 
        void btn_Click(object sender, EventArgs e) 
        { 
            try 
            { 
                Button btn = sender as Button; 
 
                switch (btn.Name) 
                { 
                    case "btnOne": 
                        txtInput.Text += "1"; 
                        break; 
                    case "btnTwo": 
                        txtInput.Text += "2"; 
                        break; 
                    case "btnThree": 
                        txtInput.Text += "3"; 
                        break; 
                    case "btnFour": 
                        txtInput.Text += "4"; 
                        break; 
                    case "btnFive": 
                        txtInput.Text += "5"; 
                        break; 
                    case "btnSix": 
                        txtInput.Text += "6"; 
                        break; 
                    case "btnSeven": 
                        txtInput.Text += "7"; 
                        break; 
                    case "btnEight": 
                        txtInput.Text += "8"; 
                        break; 
                    case "btnNine": 
                        txtInput.Text += "9"; 
                        break; 
                    case "btnZero": 
                        txtInput.Text += "0"; 
                        break; 
                    case "btnDot": 
                        if(!txtInput.Text.Contains(".")) 
                            txtInput.Text += "."; 
                        break; 
 
                } 
            } 
            catch(Exception ex) 
            { 
                MessageBox.Show("Sorry for the inconvenience, Unexpected error occured. Details: " + 
                    ex.Message); 
            } 
        } 
 
        private void txtInput_KeyPress(object sender, KeyPressEventArgs e) 
        { 
            switch (e.KeyChar) 
            { 
                case '1': 
                case '2': 
                case '3': 
                case '4': 
                case '5': 
                case '6': 
                case '7': 
                case '8': 
                case '9': 
                case '0': 
                //case '+': 
                //case '-': 
                //case '*': 
                //case '/': 
                //case '.': 
                    break; 
                default: 
                    e.Handled = true; 
                    MessageBox.Show("Only numbers, +, -, ., *, / are allowed"); 
                    break; 
            }            
        } 
 
        private void txtInput_TextChanged(object sender, EventArgs e) 
        { 
             
        } 
 
        private void btnPlus_Click(object sender, EventArgs e) 
        { 
            operand1 = txtInput.Text; 
            operation = '+'; 
            txtInput.Text = string.Empty; 
        } 
 
        private void btnMinus_Click(object sender, EventArgs e) 
        { 
            operand1 = txtInput.Text; 
            operation = '-'; 
            txtInput.Text = string.Empty; 
        } 
 
        private void btnMulitply_Click(object sender, EventArgs e) 
        { 
            operand1 = txtInput.Text; 
            operation = '*'; 
            txtInput.Text = string.Empty; 
        } 
 
        private void btnDivide_Click(object sender, EventArgs e) 
        { 
            operand1 = txtInput.Text; 
            operation = '/'; 
            txtInput.Text = string.Empty; 
        } 
 
        private void btnEqual_Click(object sender, EventArgs e) 
        { 
            operand2 = txtInput.Text; 
 
            double opr1, opr2; 
            double.TryParse(operand1, out opr1); 
            double.TryParse(operand2, out opr2); 
 
            switch (operation) 
            { 
                case '+': 
                    result = (opr1 + opr2).ToString(); 
                    break; 
 
                case '-': 
                    result = (opr1 - opr2).ToString(); 
                    break; 
 
                case '*': 
                    result = (opr1 * opr2).ToString(); 
                    break; 
 
                case '/': 
                    if (opr2 != 0) 
                    { 
                        result = (opr1 / opr2).ToString(); 
                    } 
                    else 
                    { 
                        MessageBox.Show("Can't divide by zero"); 
                    } 
                    break; 
            } 
 
            txtInput.Text = result.ToString(); 
        } 
 
        private void btnClear_Click(object sender, EventArgs e) 
        { 
            txtInput.Text = string.Empty; 
            operand1 = string.Empty; 
            operand2 = string.Empty; 
        } 
 
        private void btnSqrRoot_Click(object sender, EventArgs e) 
        { 
            double opr1; 
            if (double.TryParse(txtInput.Text, out opr1)) 
            { 
                txtInput.Text = (Math.Sqrt(opr1)).ToString(); 
            } 
        } 
 
        private void btnByTwo_Click(object sender, EventArgs e) 
        { 
            double opr1; 
            if (double.TryParse(txtInput.Text, out opr1)) 
            { 
                txtInput.Text = (opr1 / 2).ToString(); 
            } 
        } 
 
        private void btnByFour_Click(object sender, EventArgs e) 
        { 
            double opr1; 
            if (double.TryParse(txtInput.Text, out opr1)) 
            { 
                txtInput.Text = (opr1 / 4).ToString(); 
            } 
        } 
    } 
}