String类型的二进制数求和

public static string er(string a, string b)
        {
            int l;
            if (a.Length>b.Length)
            {
                l = a.Length;
            }
            else
            {
                l = b.Length;
            }
            char[] c1 = new char[l];
            char[] c2 = new char[l];
            char p='0';
            char[] c3 = new char[l + 1];
            for (int j = 0; j < l+1; j++)
            {
                c3[j] = '0';
            }
            StringReader sra = new StringReader(a);
            sra.Read(c1, 0, l);
            StringReader srb = new StringReader(b);
            srb.Read(c2, 0, l);
            sra.Close();
            srb.Close();
            for (int i= l-1; i>=0; i--)
            {
                if (c1[i]=='0'&&c2[i]=='0')
                {
                    if (p=='1')
                    {
                        c3[i + 1] = '1';
                        p = '0';
                    }
                    else
                    {
                        c3[i + 1] = '0';
                    }
                }
                else if (!(c1[i] == '1' && c2[i] == '1'))
                {
                    if (p == '1')
                    {
                        c3[i + 1] = '0';
                    }
                    else
                    {
                        c3[i + 1] = '1';
                    }
                }
                else
                {
                    if (p == '1')
                    {
                        c3[i + 1] = '1';
                    }
                    else
                    {
                        c3[i + 1] = '0';
                        p = '1';
                    }
                }
            }
            if (p=='1')
            {
                c3[0] = '1';
            }
            StringBuilder c =new StringBuilder("");
            StringWriter sw = new StringWriter(c);
            sw.Write(c3, 0, l+1);
            sw.Close();
            return c.ToString();
        }

string x = "1010101";
string y = "1101010";
Console.WriteLine(x+"+"+y+"=");
string z = "";
z = er(x, y);
Console.WriteLine(z.ToString());
Console.ReadLine();