error occuring after storing data

Question

Hi friends,

i am getting error after performing calculation and after storing data in database

The error is

 formatExeption was unhandled

Input string was not in a correct format

the error is on
  number2 = Convert.ToInt32(txtnumdays.Text);

the logic i have used to perform calculation is

 string maxleave = "";


            int number1;
            int number2;
            int returnValue = 0;
            qry = "Select MaxLeave from LeaveMaster where LeaveName = '" + cmbLeave.Text.ToString() + "' ";
            number2 = Convert.ToInt32(txtnumdays.Text);


            DBCom.getData(qry);
            if (DBCom.rdr.HasRows)
            {
                while (DBCom.rdr.Read())
                {
                    maxleave = DBCom.rdr["MaxLeave"].ToString();
                    number1 = int.Parse(maxleave);
                    returnValue = Subtract(number1, number2);
                    txtLvslft.Text = returnValue.ToString();

please help how to solve this error

thanks