How not to write something in C#

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

namespace Giant_stats_calucator
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Activate_Click(object sender, EventArgs e)
        {
            double a = TbHeight.Value;     // Human Height
            double A;                      // Giant height
            double b = TbStrength.Value;   // Human Strength
            double B;                      // Giant Strength
            double c = TbWeight.Value;     // Human Weight
            double C;                      // Giant Weight
            double d = TbMultiplier.Value; // Height Multiplier
            double f = 1;                  // Divider of weight
            double g = 1;                  // Divider of Strength
            double h = 1;                  // Multiplier  for weight
            double i = 1;                  // Multiplier for strength
            string j = "";                 // String Strength
            string k = "";                 // String Weight
            double l = 1;                  // life length calculation variable
            double m;                      // Life length min
            double n;                      // Life length max
            double o = 1;                  // Normal induvidual life length min
            double p = 1;                  // Normal induvidual life length max
            double q = 1;                  // max multiplier heigth
            double r = 1;                  // multiplier component of l

            d = d / 100;
            a = a / 100;

            switch (TbMode.Value)
            {
                case 1:
                    f = 2.5;
                    g = 3;
                    h = 3;
                    i = 3;
                    o = 70;
                    p = 125;
                    q = 18.5;
                    r = 1.5;
                    break;
                case 2:
                    f = 2.5;
                    g = 1.75;
                    h = 3;
                    i = 3;
                    o = 175;
                    p = 235;
                    q = 13.5;
                    r = 2;
                    break;
                case 3:
                    f = 1;
                    g = 1;
                    h = 2;
                    i = 3;
                    break;
                case 4:
                    f = 1;
                    g = 1;
                    h = 3;
                    i = 3;
                    break;
            }



            if (TbMode.Value != 4)
            {
                l = d * r * (d / q);
                m = Math.Round(l * o);
                n = Math.Round(l * p);
                l = Math.Round(l, 2, MidpointRounding.ToEven);
                lblpotage.Text = "Expected life length is " + m + " to " + n + " years." + "   (" + l + ")";
            }
            else
                lblpotage.Text = "She can never die of age or mortal harm";


            A = a * d;

            B = System.Math.Pow(d, h) * b / g;
            C = System.Math.Pow(d, i) * c / f;

            if (B > 1000000)
            {
                B = B / 1000000;
                j = "M Kg";
            }
            else
            {
                B = B / 1000;
                j = "T";
            }

            if (C > 1000000)
            {
                C = C / 1000000;
                k = "M Kg";
            }
            else
            {
                C = C / 1000;
                k = "T";
            }
            A = Math.Round(A, 2);
            B = Math.Round(B, 2);
            C = Math.Round(C, 2);

            lblMultiplier.Text = "" + d;
            lblHeightHuman.Text = a + "m";
            lblStrengthHuman.Text = b + "Kg";
            lblWeightHuman.Text = c + "Kg";
            lblHeight.Text = "Height: " + A + "m";
            lblStrength.Text = "Strength: " + B + j;
            lblWeight.Text = "Weight: " + C + k;
        }

        protected override void OnShown(EventArgs e)
        {
            Activate.PerformClick();
            lblMode.Text = "Giants";

        }
        private void TbHeight_Scroll(object sender, EventArgs e)
        {
            double a = TbHeight.Value;     // Height no dividing
            double c = 300;                // Strength max human
            double d = 125;                // weigth max human
            double g = 230;                // Max human heigth
            double f = 100;                // Min human heigth
            double j = 20;                 // Min weigth human
            double k = 30;                 // Min strength human
            double l;                      // Calc 1
            double m;                      // Calc 2
            double n;                      // Calc 3
            double o;                      // Calc 4
            double p;
            double q;

            switch (TbMode.Value)
            {
                case 2:
                    c = 250;
                    d = 75;
                    f = 100;
                    g = 165;
                    j = 20;
                    k = 30;
                    break;
                case 3:
                    c = 250;
                    d = 130;
                    f = 100;
                    g = 230;
                    j = 20;
                    k = 30;
                    break;
                case 4:
                    c = 187;
                    d = 63;
                    f = 177;
                    g = 179;
                    j = 61;
                    k = 185;
                    break;
            }

            if (TbMode.Value != 4)
            {
                double t = (a) / (g);
                double u = (a) / (f);

                l = (c * t);
                m = (k * u);
                n = (d * t);
                o = (j * u);

                TbStrength.Maximum = (int)l;
                TbStrength.Minimum = (int)m;
                TbStrength.Value = (int)((l + m) / 2);

                TbWeight.Maximum = (int)n;
                TbWeight.Minimum = (int)o;
                TbWeight.Value = (int)((n + o) / 2);

            }
            else
            {
                TbStrength.Maximum = 187;
                TbStrength.Minimum = 185;
                TbStrength.Value = 186;

                TbWeight.Maximum = 63;
                TbWeight.Minimum = 61;
                TbWeight.Value = 62;
            }
            Activate.PerformClick();
        }

        private void TbStrength_Scroll(object sender, EventArgs e)
        {

            Activate.PerformClick();
        }

        private void TbWeight_Scroll(object sender, EventArgs e)
        {

            Activate.PerformClick();
        }

        private void TbMultiplier_Scroll(object sender, EventArgs e)
        {

            Activate.PerformClick();
        }

        private void TbMode_Scroll(object sender, EventArgs e)
        {
            int b = 1850;           // Positive multiplier component min
            int c = 1300;           // Positive multiplier component max
            int d = 300;            // Max strength giants
            int f = 30;             // Min strength giants
            int g = 125;            // Max weight giants
            int h = 20;             // Min weight giants

            switch (TbMode.Value)
            {
                case 1: // Giants
                    TbHeight.Maximum = 225;
                    TbHeight.Minimum = 100;
                    TbHeight.Value = 170;

                    lblMode.Text = "Giants";
                    TbMultiplier.TickFrequency = 150;
                    break;
                case 2: // Tigrissess
                    d = 250;
                    f = 50;
                    g = 75;
                    h = 25;
                    b = 1350;
                    c = 1050;

                    TbHeight.Maximum = 165;
                    TbHeight.Minimum = 100;
                    TbHeight.Value = 140;

                    lblMode.Text = "Giant Tigri";
                    TbMultiplier.TickFrequency = 100;
                    break;
                case 3: // Realistic
                    d = 250;
                    f = 50;
                    g = 130;
                    h = 30;
                    b = 5000;
                    c = 500;

                    TbHeight.Maximum = 225;
                    TbHeight.Minimum = 100;
                    TbHeight.Value = 175;
                    lblMode.Text = "Realistic giants";
                    TbMultiplier.TickFrequency = 750;
                    break;
                case 4: // Avina
                    d = 187;
                    f = 185;
                    g = 63;
                    h = 61;
                    b = 4051;
                    c = 4049;

                    TbHeight.Maximum = 179;
                    TbHeight.Minimum = 177;
                    TbHeight.Value = 178;
                    lblMode.Text = "Avina ";
                    TbMultiplier.TickFrequency = 1;
                    break;
            }
            TbStrength.Maximum = d;
            TbStrength.Minimum = f;
            TbStrength.Value = (d + f) / 2;

            TbWeight.Maximum = g;
            TbWeight.Minimum = h;
            TbWeight.Value = (g + h) / 2;

            TbMultiplier.Maximum = b;
            TbMultiplier.Minimum = c;
            TbMultiplier.Value = (b + c) / 2;

            Activate.PerformClick();
        }

        private void Round_Click(object sender, EventArgs e)
        {
            double a = TbMultiplier.Value;
            double A;

            a = a / 100;
            try
            {
                A = Math.Round((double)a, 1, MidpointRounding.ToEven);

                if (A == a)
                    A = Math.Round((double)a, MidpointRounding.ToEven);
                A = A * 100;

                TbMultiplier.Value = Convert.ToInt32(A);
            }
            catch (ArgumentOutOfRangeException)
            { }
            Activate.PerformClick();
        }

        private void CB_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}