void Band_4()
        {
            if (comboBox1.Text == "4")
            {
                if (textBox1.Text == "0")
                {
                    MessageBox.Show("Otpornost mora biti veca od nule!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }
                if (comboBox2.Text == "")
                {
                    MessageBox.Show("Izaberi vrednost tolerancije!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }
                List<double> E6 = new List<double> { 1, 1.5, 2.2, 3.3, 4.7, 6.8, 10 };
                List<double> E12 = new List<double> { 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, 10 };
                List<double> E24 = new List<double> { 1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, 10 };
                var colours = new string[] { "Black", "Brown", "Red", "Orange", "Yellow", "Green", "Blue", "Violet", "Grey", "White", "Silver", "Gold" };
                var factorDictionary = new Dictionary<char, double>() { { 'p', 0.000000000001 }, { 'n', 0.000000001 }, { 'u', 0.000001 }, { 'm', 0.001 }, { 'R', 1 }, { 'K', 1000 }, { 'M', 1000000 }, { 'G', 1000000000 } };
                string res = string.Empty;

                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 (comboBox2.Text == "E12 (10%)")
                {
                    for (int i = 0; i < E12.Count; i++)
                    {
                        if (isUnitCorrect && isValueCorrect)
                        {
                            double mul = factorDictionary[lastChar];
                            double val = double.Parse(value) * mul;
                            min = mul * E12[0];
                            p = mul * E12[i];
                            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)
                                {
                                    r = Math.Abs(p - val);
                                    /* r = p - val;
                                     if(r<)*/
                                    label5.Text = Convert.ToString(p);
                                }
                            }

                            res = val.ToString();

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

                            else
                            {
                                label15.BackColor = Color.FromName(colours[res[0] - '0']);
                                label16.BackColor = Color.FromName(colours[res[1] - '0']);
                                label17.BackColor = Color.FromName(colours[third != 0 ? third : res.Count() - 2]);
                                label6.Text = textBox1.Text;
                                textBox2.Text = colours[res[0] - '0'];
                                textBox3.Text = colours[res[1] - '0'];
                                textBox4.Text = colours[third != 0 ? third : res.Count() - 2];
                                //label5.Text = Convert.ToString(p);
                            }
                        }
                        if (comboBox1.Text == "4")
                        {
                            if (comboBox2.Text == "E24 (5%)")
                            {
                                label18.BackColor = Color.Gold;
                                textBox5.Text = "Gold";
                            }
                            if (comboBox2.Text == "E12 (10%)")
                            {
                                label18.BackColor = Color.Silver;
                                textBox5.Text = "Silver";
                            }
                        }
                    }
                }
                else
                {
                    MessageBox.Show("Invalid value!", "Otpornost", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }
            }
        }