logic not working after retrieving data from database

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C#

SQL-Server

private void textBox10_Click(object sender, EventArgs e)
        {
            int a = 0, b = 0, c = 0;

            if (!int.TryParse(textBox8.Text,
                                System.Globalization.NumberStyles.Integer,
                                System.Globalization.CultureInfo.CurrentUICulture,
                                out a))
            {
                MessageBox.Show("u need to enter value");
            }
            else if (!int.TryParse(textBox9.Text,
                                    System.Globalization.NumberStyles.Integer,
                                    System.Globalization.CultureInfo.CurrentUICulture,
                                    out b) || (b > a))
            {
                MessageBox.Show("u entered greater value");
            }
            else
            {
                c = a - b;
                textBox10.Text = c.ToString(
                    System.Globalization.CultureInfo.CurrentUICulture);
            }

               
        }

while inserting data..this code performing subtraction correctly, then i just retrieved "added" data from DB using search query.. now textbox8,9,10 will have fetched data from DB like 12,8,4... now if i change the value of textbox9 and textbox8 and click textbox10 it need to perform subtraction(click event for textbox10) but its not performing simply MessageBox in first if statement displaying...
why this happening