Question

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

  namespace Adaline
  {
  public partial class Form1 : Form
  {
    float d1, d2, d3, d4, eta;
    float y1, y2, y3, y4;
    float w10, w11, w12;
    float w20, w21, w22;
    float w30, w31, w32;
    float w40, w41, w42;
    float x10, x11, x12;
    float x20, x21, x22;
    float x30, x31, x32;
    float x40, x41, x42;

    float net, net1, net2, net3, net4;

    float dw10, dw11, dw12;
    float dw20, dw21, dw22;
    float dw30, dw31, dw32;
    float dw40, dw41, dw42;

        public Form1()
    {
        InitializeComponent();
    }
        public void Adaline(float x0, float x1, float x2,
                            float w0, float w1, float w2,
                            float d, float net, float y,
                            float dw0, float dw1, float dw2, float eta)
        {
            net = x0 * w0 + x1 * w1 + x2 * w2;

            if (net <= 0)
                y = 1;
            else
                y = -1;

            dw0 = eta * x0 * (d - net);
            dw1 = eta * x1 * (d - net);
            dw2 = eta * x2 * (d - net);

            string a = "{0}   {1}   {2}   {3}   {4}    {5}   {6}   {7}   {8}    {9}     {10}    {11}", x0, x1, x2, w0, w1, w2, d, net, y, dw0, dw1, dw2;
            listBox1.Items.Add(a);
        }

    private void button1_Click(object sender, EventArgs e)
    {
        eta = Convert.ToSingle(textBox20);

        d1 = Convert.ToSingle(textBox19);
        d2 = Convert.ToSingle(textBox18);
        d3 = Convert.ToSingle(textBox17);
        d4 = Convert.ToSingle(textBox16);

        w10 = Convert.ToSingle(textBox3);
        w11 = Convert.ToSingle(textBox2);
        w12 = Convert.ToSingle(textBox1);
        int passes = 0;

        x10 = Convert.ToSingle(textBox7);
        x11 = Convert.ToSingle(textBox11); 
        x12 = Convert.ToSingle(textBox15);
        x20 = Convert.ToSingle(textBox6);
        x21 = Convert.ToSingle(textBox10);
        x22 = Convert.ToSingle(textBox14);
        x30 = Convert.ToSingle(textBox5);
        x31 = Convert.ToSingle(textBox9);
        x32 = Convert.ToSingle(textBox13);
        x40 = Convert.ToSingle(textBox4);
        x41 = Convert.ToSingle(textBox8);
        x42 = Convert.ToSingle(textBox12);

        while (passes <= 100)
        {
            Adaline(x10, x11, x12, w10, w11, w12, d1, net1, y1, dw10, dw11, dw12, eta);

            w20 = w10 + dw10;
            w21 = w11 + dw11;
            w22 = w12 + dw12;

            Adaline(x20, x21, x22, w20, w21, w22, d2, net2, y2, dw20, dw21, dw22, eta);

            w30 = w20 + dw20;
            w31 = w21 + dw21;
            w32 = w22 + dw22;

            Adaline(x30, x31, x32, w30, w31, w32, d3, net3, y3, dw30, dw31, dw32, eta);

            w40 = w30 + dw30;
            w41 = w31 + dw31;
            w42 = w32 + dw32;

            Adaline(x40, x41, x42, w40, w41, w42, d4, net4, y4, dw40, dw41, dw42, eta);

            w10 = w40 + dw40;
            w11 = w41 + dw41;
            w12 = w42 + dw42;

            passes += 1;
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {

    }

}

}

I get thiese errors:
1 Cannot use local variable ‘net’ before it is declared. The declaration of the local variable hides the field ‘Adaline.Form1.net’
2 Cannot use local variable ‘x0’ before ot os declared.
3 Cannot use local variable ‘w0’ before ot os declared.
4 Cannot use local variable ‘x1’ before ot os declared.
.
.
.

Answer 1

The second error is the cause of the other errors.

You have declared a method parameter with the same name as a method field. That hides the field inside the method.

That error causes the parameters not to be declared correctly, and you get another error for each time you use one of the parameters in the method.