operator += cannot be applied with string and void asp.net

Question

User-367318540 posted

following error is coming

operator += cannot be applied with string and void asp.net

on this below line

 

 ResultValue +=Convert.ToString(this.InsertRows(s_No, v_Name, rate, s_liter, entryDate);

below is my whole code

string s_No, v_Name, rate, s_liter, entryDate, ResultValue = Convert.ToString(0); 

                foreach (DataRow row in dt.Rows)
                {


                    s_No = (row["S_No"].ToString());
                    v_Name = (row["V_Name"].ToString());
                    rate = (row["Rate"].ToString());
                    s_liter = (row["S_liter"].ToString());
                    entryDate = (row["EntryDate"].ToString());
                    ResultValue +=Convert.ToString(this.InsertRows(s_No, v_Name, rate, s_liter, entryDate);
                }
                if (ResultValue == dt.Rows.Count)
                {
                    // Response.Redirect("BalePack.aspx");
                    Response.Redirect("Packrpt.aspx?PID=" + I_ID + "");
                }
                else
                {
                    Response.Write("<script>alert('Not Save'</script>");
                }
            }
        }
        
        private void InsertRows(string s_No, string v_Name, string rate, string s_liter, string entryDate)
        {
            //con.Open();
            using (SqlCommand cmd = new SqlCommand("Sp_InsertInvM", con))
            {
                cmd.Parameters.AddWithValue("@Action", "INSERTD");
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@I_ID", I_ID);
                cmd.Parameters.AddWithValue("@S_Date", entryDate);
                cmd.Parameters.AddWithValue("@S_No", s_No);
                cmd.Parameters.AddWithValue("@P_Price", rate);
                cmd.Parameters.AddWithValue("@S_Liter", s_liter);

                con.Open();
                cmd.ExecuteNonQuery();

                ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", " alert('Duplicate Order Save SuccessFully.'); window.open('SOgvud.aspx');", true);

                con.Close();

Answer 1

User753101303 posted

Hi,

InsertRows doesn"t return any value (void). It seems you want to use 

ResultValue +=this.InsertRows(s_No, v_Name, rate, s_liter, entryDate);

And have InsertRows to return the value returned by cmd.ExecuteNonQuery ?

Answer 2

User415553908 posted

Convert.ToString() needs an object to work with. The function you use as its argument does not return anything at all: private void InsertRows(...), resulting in the exception you see.

Looking at your code, it seems you are trying to verify how many rows your stored proc processed. You could modify it to look something along these lines:

string s_No, v_Name, rate, s_liter, entryDate;
int ResultValue = 0;

foreach (DataRow row in dt.Rows)
{
	s_No = (row["S_No"].ToString());
	v_Name = (row["V_Name"].ToString());
	rate = (row["Rate"].ToString());
	s_liter = (row["S_liter"].ToString());
	entryDate = (row["EntryDate"].ToString());
	ResultValue += this.InsertRows(s_No, v_Name, rate, s_liter, entryDate); // no conversion needed 
}
if (ResultValue == dt.Rows.Count)
{
	// Response.Redirect("BalePack.aspx");
	Response.Redirect("Packrpt.aspx?PID=" + I_ID + "");
}
else
{
	Response.Write("<script>alert('Not Save'</script>");
}
            
private int InsertRows(string s_No, string v_Name, string rate, string s_liter, string entryDate)
{
	//con.Open();
	using (SqlCommand cmd = new SqlCommand("Sp_InsertInvM", con))
	{
		cmd.Parameters.AddWithValue("@Action", "INSERTD");
		cmd.CommandType = CommandType.StoredProcedure;
		cmd.Parameters.AddWithValue("@I_ID", I_ID);
		cmd.Parameters.AddWithValue("@S_Date", entryDate);
		cmd.Parameters.AddWithValue("@S_No", s_No);
		cmd.Parameters.AddWithValue("@P_Price", rate);
		cmd.Parameters.AddWithValue("@S_Liter", s_liter);

		con.Open();
		int result = cmd.ExecuteNonQuery(); // get the value from your stored proc (I assume you want first value of the first result set it returns as per documentation: https://docs.microsoft.com/en-us/dotnet/api/microsoft.data.sqlclient.sqlcommand.executenonquery?view=sqlclient-dotnet-1.1)

		ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", " alert('Duplicate Order Save SuccessFully.'); window.open('SOgvud.aspx');", true);

		con.Close();
		return result; // return a value
}

Performance suggestion: since you concatenate string in a foreach loop, you might want to consider using StringBuilder instead