Operator '*' cannot be applied to operands of type 'string' and 'string'

Question

 }
        public void SaveBillDetails(BillDetail details)
        {
            SqlConnection con = new SqlConnection(ConnectionString);
            try
            {
                
                con.Open();
                SqlCommand cmd = new SqlCommand("spt_saveEBillDetails", con);
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@CustomerName",details.CustomerName);
                cmd.Parameters.AddWithValue("@MobileNumber",details.MobileNumber);
                cmd.Parameters.AddWithValue("@Address",details.Address);
                cmd.Parameters.AddWithValue("@TotalAmount",details.TotalAmount);

                SqlParameter outputPara = new SqlParameter();
                outputPara.DbType = DbType.Int32;
                outputPara.Direction = ParameterDirection.Output;
                outputPara.ParameterName = "@Id";
                cmd.Parameters.Add(outputPara);
                cmd.ExecuteNonQuery();
                int id = int.Parse(outputPara.Value.ToString());
                if(details.Items.Count> 0)

Note : Please help out guru............ Thanks

details.TotalAmount = details.Items.Sum(i => i.Price * i.Quantity); // This is where my issue is

Answer 1

Check this:

details.TotalAmount = details.Items.Sum(i => decimal.Parse(i.Price) * int.Parse(i.Quantity));

Or maybe adjust the types of Price and Quantity.

Answer 2

No need to use decimal.Parse or int.Parse conceptual example

SET ANSI_NULLS ON;
GO
SET QUOTED_IDENTIFIER ON;
GO

CREATE PROCEDURE spDemo @Parm DECIMAL(18, 2) OUT
AS
BEGIN
    SET NOCOUNT ON;
    SET @Parm = 93.77;
END;
GO

Code

public static void StoredDemo()
{
    using var cn = new SqlConnection(ConnectionString());
    using var cmd = new SqlCommand("spDemo", cn);

    cmd.CommandType = CommandType.StoredProcedure;

    cmd.Parameters.Add("@Parm", SqlDbType.Decimal)
        .Direction = ParameterDirection.Output;
    
    
    cn.Open();
    cmd.ExecuteNonQuery();
    int quantity = 10;
    decimal value = (decimal)cmd.Parameters["@Parm"].Value ;
    decimal result = value * quantity;
}

Answer 3

Thanks for your contributions @Viorel and @Karen

I used this below and it worked for me

details.TotalAmount = details.Items.Sum(i => int.Parse(i.Price) * int.Parse(i.Quantity));

I converted both strings to int using parse..