bank account to account transaction in c#

SqlConnection con = new SqlConnection("server=.; database=bank; user id=sa; password=;");

private void button1_Click(object sender, EventArgs e)

{

int fano, tano, bal;

fano = int.Parse(textBox1.Text);

tano = int.Parse(textBox2.Text);

bal = int.Parse(textBox3.Text);

 

 

SqlCommand cmd = con.CreateCommand();

SqlTransaction transaction = null;

try

{

con.Open();

transaction = con.BeginTransaction();

cmd.Transaction = transaction;

cmd.CommandText = "update accountholder set Balance= '"+bal+"'-Balance where acno= '" + textBox1.Text + "'";

cmd.ExecuteNonQuery();

cmd.CommandText = "update accountholder set Balance= '" + bal + "'+ Balance where acno= '" + textBox2.Text + "'";

cmd.ExecuteNonQuery();

cmd.CommandText = "insert into TransferDetails (acno1,acno2,Balance) VALUES (@acno1,@acno2,@Balance)";

cmd.Parameters.AddWithValue("@acno1", textBox1.Text);

cmd.Parameters.AddWithValue("@acno2", textBox2.Text);

cmd.Parameters.AddWithValue("@Balance", textBox3.Text);

cmd.ExecuteNonQuery();

MessageBox.Show("suceess");

transaction.Commit();

}

catch(Exception ex)

{

transaction.Rollback();

MessageBox.Show(ex.Message);

}

finally

{

con.Close();

}

}

 

I wanted to transfer money from one account to another. The error occurred is SQL syntax based on where clause.i have atached the source code also. please correct the error 

this line were getting error while running the code thanks