calculator/Form1.cs

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

namespace WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double a, b;
        int count;
        bool pr = false;
        bool min = true;
        private void очиститьToolStripMenuItem_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
            label1.Text= string.Empty;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 1;
           
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 2;
           
        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 3;
           
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 4;
            
        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 5;
            
        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 6;
            
        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 7;
            
        }

        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 8;
            
        }

        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 9;
            
        }

        private void button13_Click(object sender, EventArgs e)
        {
            if (pr == false)
            {
                a = double.Parse(textBox1.Text);
                textBox1.Clear();
            }
            count = 1;
            label1.Text = a.ToString() + "+";
            pr = true;
            min = true;
        }

        private void button12_Click(object sender, EventArgs e)
        {
            if (pr == false)
            {
                a = double.Parse(textBox1.Text);
                textBox1.Clear();
            }
            count = 2;
            label1.Text = a.ToString() + "-";
            pr = true;
            min = true;
        }

        private void button14_Click(object sender, EventArgs e)
        {
            if (pr == false)
            {
                a = double.Parse(textBox1.Text);
                textBox1.Clear();
            }
            count = 3;
            label1.Text = a.ToString() + "*";
            pr = true;
            min = true;
        }

        private void button15_Click(object sender, EventArgs e)
        {
            if (pr == false)
            {
                a = double.Parse(textBox1.Text);
                textBox1.Clear();
            }
            count = 4;
            label1.Text = a.ToString() + "/";
            pr = true;
            min = true;
        }

        private void button10_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
            label1.Text = string.Empty;
        }

        private void button11_Click(object sender, EventArgs e)
        {
            label1.Text = string.Empty;

            switch (count)
            {
                case 1:
                    b = a + double.Parse(textBox1.Text);
                    textBox1.Text = b.ToString();
                    break;
                case 2:
                    b = a - double.Parse(textBox1.Text);
                    textBox1.Text = b.ToString();
                    break;
                case 3:
                    b = a * double.Parse(textBox1.Text);
                    textBox1.Text = b.ToString();
                    break;
                case 4:

                    double nol;
                    nol = double.Parse(textBox1.Text);
                    if (nol == 0.0)
                    {
                        MessageBox.Show("Делить на ноль нельзя!");
                    }

                    b = a / double.Parse(textBox1.Text);
                    textBox1.Text = b.ToString();
                    break;
                default:
                    break;
            }
            pr = false;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button17_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.IndexOf(',') == -1)
            {
                textBox1.Text += ",";
            }
        }

        private void button18_Click(object sender, EventArgs e)
        {
            int lenght = textBox1.Text.Length - 1;
            string text = textBox1.Text;
            textBox1.Clear();
            for (int i = 0; i < lenght; i++)
            {
                textBox1.Text = textBox1.Text + text[i];
            }
        }

        private void button19_Click(object sender, EventArgs e)
        {
            if (min == true)
            {
                textBox1.Text = "-" + textBox1.Text;
                min = false;
            }
            else if (min == false)
            {
                textBox1.Text = textBox1.Text.Replace("-", "");
                min = true;
            }
        }

        private void button16_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + 0;
        }
    }
}