MainFormApp.cs

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

namespace SuggestNumbersApp
{
    public partial class MainFormApp : Form
    {
        public MainFormApp()
        {
            InitializeComponent();
        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            Accuracy.Visible = !IntegersOnly.Checked;

            RecalculateSuggestedType();
        }

        private void checkBox3_CheckedChanged(object sender, EventArgs e)
        {
            RecalculateSuggestedType();
        }

        private void textBox_TextChanged(object sender, EventArgs e)
        {
            RecalculateSuggestedType();
            ValidateMinAndMaxValue();
        }

        private void RecalculateSuggestedType()
        {
            if (isInputComplete())
            {
                var minValue = BigInteger.Parse(textBox1.Text);
                var maxValue = BigInteger.Parse(textBox2.Text);

                if (maxValue >= minValue)
                {
                    SuggestedTypeResult.Text =
                        NumericTypeSuggester.GetName(
                            minValue,
                            maxValue,
                            IntegersOnly.Checked,
                            Accuracy.Checked);
                    return;
                }
            }
            SuggestedTypeResult.Text = "Не хватает данных!";
        }

        private void ValidateMinAndMaxValue()
        {
            bool isValid = true;

            if(isInputComplete())
            {
                var minValue = BigInteger.Parse(textBox1.Text);
                var maxValue = BigInteger.Parse(textBox2.Text);

                if (maxValue < minValue)
                {
                    isValid = false;
                }
            }

            textBox2.BackColor = isValid ? Color.White : Color.MediumVioletRed;
        }

        private bool isInputComplete()
        {
            return textBox1.Text.Length > 0 && textBox1.Text != "-" &&
                   textBox2.Text.Length > 0 && textBox2.Text != "-";
        }

        private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
        {
            var textBox = (TextBox)sender;
            if(!IsValidInput(e.KeyChar, textBox)) {
                e.Handled = true;
            }
        }

        private bool IsValidInput(char keyChar, TextBox textBox)
        {
            return char.IsControl(keyChar) || char.IsDigit(keyChar) ||
                (keyChar == '-' && textBox.SelectionStart == 0);
        }

        private void label2_Click(object sender, EventArgs e)
        {
            
        }

        private void SuggestedTypeResult_Click(object sender, EventArgs e)
        {

        }
    }
}