public void Band_4()
        {
            if (radioButton1.Checked)
            {
                if (textBox1.Text == "0")
                {
                    MessageBox.Show("Otpornost mora biti veca od nule!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }
                if (comboBox1.Text == "")
                {
                    MessageBox.Show("Izaberi vrednost tolerancije!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }

                while (string.IsNullOrEmpty(res))
                {
                    res = textBox1.Text;
                }

                var lastChar = res.Last();
                var isUnitCorrect = factorDictionary.ContainsKey(lastChar);
                var value = res.Substring(0, res.Length - 1);
                var isValueCorrect = !value.Any(x => !char.IsDigit(x));

                        if (isUnitCorrect && isValueCorrect)
                        {
                            double mul = factorDictionary[lastChar];
                            double val = double.Parse(value) * mul;
                            int third = 0;

                    if (val < 0.1)
                            {
                                MessageBox.Show("Otpornost ne moze da bude manja od 0.1 oma!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                return;
                            }
                            if (val < 1)
                            {
                                val *= 100;
                                third = 10;
                            }
                            else if (val < 10)
                            {
                                val *= 10;
                                third = 11;
                            }


                            /*if (p <= val)
                            {
                                if (p < min)
                                {
                                    min = E12[i];
                                    r = Math.Abs(val - p);
                                }
                            }*/

                            res = val.ToString();

                            if (res.Count() > 24)
                            {
                                MessageBox.Show("Pogresna vrednost!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                return;
                            }

                            else
                            {
                                label14.BackColor = Color.FromName(colours[res[0] - '0']);
                                label15.BackColor = Color.FromName(colours[res[1] - '0']);
                                label16.BackColor = Color.FromName(colours[third != 0 ? third : res.Count() - 2]);
                                label4.Text = textBox1.Text;
                                textBox2.Text = colours[res[0] - '0'];
                                textBox3.Text = colours[res[1] - '0'];
                                textBox4.Text = colours[third != 0 ? third : res.Count() - 2];
                            }
                        }
                        if (radioButton1.Checked)
                        {
                            if (comboBox1.Text == "E24 (5%)")
                            {
                                label17.BackColor = Color.Gold;
                                textBox5.Text = "Gold";
                            }
                            if (comboBox1.Text == "E12 (10%)")
                            {
                                label17.BackColor = Color.Silver;
                                textBox5.Text = "Silver";
                            }
                        }
                    }
                }