Getting Error : Use of unassigned local variable

From your code it is quite clear that you have not assigned any value to k1.
So change the 3rd line of your code like below.

int k1 = 0, k2 = 0;

Hello use this code as like


public DataSet wsGenerateBill(string OrderID)
{
string total1 = string.Empty;
float FinalTotal = 0;
int k1=0;
int k2 = 0;
try
{
DataSet ds = new DataSet();
SqlCommand cmd = new SqlCommand("SELECT OrderDetails.FoodID, OrderDetails.Qty, OrderDetails.Price, OrderDetails.Qty * OrderDetails.Price AS Total From OrderDetails Where (OrderID = '" + OrderID + "')", con);
con.Open();
SqlDataReader sdr = cmd.ExecuteReader();
DataTable dt = new DataTable();
dt.Load(sdr);
con.Close();

int m = od1.UpdateTotalAmtOfFood(OrderID);

if (dt.Rows.Count == 0)
{
return null;
}
else
{
for( int i =0; i < dt.Rows.Count; i++)
{
DataRow dr = dt.Rows[i];
string foodid = dr["FoodID"].ToString();
string quantity = dr["Qty"].ToString();
string price = dr["Price"].ToString();
string total = dr["Total"].ToString();

int quantity1 = int.Parse(quantity);
int price1 = int.Parse(price);
float billtotal = float.Parse(total);

FinalTotal = FinalTotal + billtotal;
}
object outletid = orders.getOutletIDByOrderID(OrderID);
string outletid1 = (string)outletid;

object exist = bill.getBillIDByOrderID(OrderID);

if (exist == null)
k1 = bill.CreateBill(OrderID, outletid1, FinalTotal,'0','0');

if (k1 > 0)
k2 = bill.UpdateGrandTotalOfBill(OrderID);


SqlCommand cmd1 = new SqlCommand("SELECT Bill.BillID, Bill.OutletID, Bill.OrderID, [Order].CustomerID, Customer.Name AS CustomerName, [Order].DestinationPlace, [Order].VehicleNo, [Order].SeatNo, [Order].PaymentMode, [Order].OrderDate, [Order].DeliveryTime, [Order].DeliveryDate, Outlet.Name AS OutletName, Outlet.City AS OutletCity, OrderDetails.FoodID, Food.Name AS FoodName, OrderDetails.Qty, OrderDetails.Price, OrderDetails.Total AS FoodTotal, Bill.OrderTotalAmt, Bill.TaxAmt, Bill.GrandTotal FROM Bill INNER JOIN [Order] ON Bill.OrderID = [Order].OrderID INNER JOIN Customer ON [Order].CustomerID = Customer.CustomerID INNER JOIN Outlet ON Bill.OutletID = Outlet.OutletID INNER JOIN OrderDetails ON [Order].OrderID = OrderDetails.OrderID INNER JOIN Food ON OrderDetails.FoodID = Food.FoodID WHERE (Bill.OrderID = '" + OrderID + "')", con);
con.Open();
SqlDataReader sdr1 = cmd1.ExecuteReader();
DataSet ds1 = new DataSet();
DataTable dt1 = new DataTable();
dt1.Load(sdr1);
con.Close();

if (dt1.Rows.Count == 0)
{
DataTable table1 = new DataTable("Bill");
table1.Columns.Add("Result");
table1.Rows.Add("Null");
ds1.Tables.Add(table1);
return ds1;
}
else
{
ds1.Tables.Add(dt1);
return ds1;
}
}
}
catch (Exception)
{
return null;
}
}