This code for binary to decimal. I didint see like this easy code. The other calculating codes are too long and complex. I made this and you can use easily.

private void button1_Click(object sender, EventArgs e)
{
if (textBox1.Text.Length > 0)
{
string sayii = textBox1.Text.Substring(0, textBox1.Text.Length);
uint[] sayicc = new uint[textBox1.Text.Length];

            for (int i = 0; i < textBox1.Text.Length; i++)
            {
                sayicc\[i\] = Convert.ToUInt32(sayii\[i\] - 48);

            }

            uint\[\] dizi2 = new uint\[textBox1.Text.Length\];
            uint bit = 1;

            for (int j = 0; j < textBox1.Text.Length; j++)
            {
                dizi2\[j\] = bit;
                bit \*= 2;
            }
            Array.Reverse(dizi2);
            uint deger = 0;
            for (int i = 0; i <= dizi2.Length - 1; i++)
            {
                dizi2\[i\] \*= sayicc\[i\];

                if (sayicc\[i\] == 1)
                {
                    deger += dizi2\[i\];
                }
            }
            textBox2.Text = "  " + deger.ToString();
        }
        else
        {
            MessageBox.Show("Deger girilecek alan boş.", "HATA!!!", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }