New user. Variables question.

Question

Hello I've just started learning C# and I'm having some troubles getting a grip on how variables are used. I've building a web app to access a SQL database to retrieve data and insert data. I built it using a tutorial I found in the Microsoft help files. Anyway what I want to do is retrieve data from some fields in a table store the values in variables and then re-write the values to a table. I declared a variable at the beginning of the class... public String Qty; ...and I'm able to use the variable in any method. However I want to be able to add a value to the variable in one method and then use it in another method to insert data to the table. I'm unable to retain the value outside of the method that it is assigned in. Any insight would be greatly appreciated.

tdiddy67 · Answer

Yes that is the line that causes the error. I can give 'Qty' a value inside the method and it will work but not outside. thanks

Carlos Sanchez · Answer

can you please put a label and assign the value of Qty to the label in 'btnGet'? And one question: the below line is which throws the exeption? cmdSOInsert.Parameters[@Qty].Value = Qty;) I want to make sure that the variable is the problem.

tdiddy67 · Answer

huh? I guess I mean to give Qty a value in 'btnGet' (Qty = dreader[8].ToString();) and hold the value for use in btnSave (cmdSOInsert.Parameters[@Qty].Value = Qty;) but it gives me an error saying no value is assigned. the web page is http://www.nwmx.net/C_PM_Data2/ you can enter 99991 as the so#. The idea is for a user to enter the amount of parts completed a user id and Y or N in the 'Complete?' field. I want some data to be retrieved but not shown to the user just written back to a table. I know there are other ways to do it but I need to learn about variables. thanks

Carlos Sanchez · Answer

What is the problem? Is thrown an exception? which line throws it? I can't see any wrong line.

tdiddy67 · Answer

This is the code for the aspx.cs file using System; using System.Collections; using System.ComponentModel; using System.Data; using System.Drawing; using System.Web; using System.Web.SessionState; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.HtmlControls; namespace C_PM_Data2 { /// /// Summary description for WebForm1. /// public class WebForm1 : System.Web.UI.Page { public string Qty; protected System.Data.SqlClient.SqlCommand cmdSOID; protected System.Data.SqlClient.SqlCommand cmdSOUpdate; protected System.Web.UI.WebControls.TextBox txtSOID; protected System.Web.UI.WebControls.TextBox txtCust; protected System.Web.UI.WebControls.Button btnGet; protected System.Web.UI.WebControls.Label lblNtrSO; protected System.Web.UI.WebControls.Label lblCust; protected System.Web.UI.WebControls.TextBox txtPartNum; protected System.Web.UI.WebControls.TextBox txtGood; protected System.Web.UI.WebControls.TextBox txtScrap; protected System.Web.UI.WebControls.TextBox txtRunTime; protected System.Web.UI.WebControls.TextBox txtOper; protected System.Web.UI.WebControls.TextBox txtDone; protected System.Web.UI.WebControls.Button btnSave2; protected System.Web.UI.WebControls.Label lblPart; protected System.Web.UI.WebControls.Label lblGood; protected System.Web.UI.WebControls.Label lblScrap; protected System.Web.UI.WebControls.Label lblRunTime; protected System.Web.UI.WebControls.Label lblComp; protected System.Web.UI.WebControls.Label lblOper; protected System.Data.SqlClient.SqlCommand cmdSOInsert; protected System.Data.SqlClient.SqlConnection sqlConnection1; public void Page_Load(object sender System.EventArgs e) { } #region Web Form Designer generated code override protected void OnInit(EventArgs e) { // // CODEGEN: This call is required by the ASP.NET Web Form Designer. // InitializeComponent(); base.OnInit(e); } /// /// Required method for Designer support - do not modify /// the contents of this method with the code editor. /// private void InitializeComponent() { this.sqlConnection1 = new System.Data.SqlClient.SqlConnection(); this.cmdSOID = new System.Data.SqlClient.SqlCommand(); this.cmdSOUpdate = new System.Data.SqlClient.SqlCommand(); this.cmdSOInsert = new System.Data.SqlClient.SqlCommand(); this.btnGet.Click += new System.EventHandler(this.btnGet_Click); this.btnSave2.Click += new System.EventHandler(this.btnSave2_Click); // // sqlConnection1 // this.sqlConnection1.ConnectionString = data source=DELL-WEB1;initial catalog=NWMX;persist security info=False;user id=sa + ;workstation id=DELL-WEB1;packet size=4096; // // cmdSOID // this.cmdSOID.CommandText = SELECT SONum CUSTOMER SUBS_QTY YIELD QTY SHIPDATE MASTER# PARTNUM COMPLET + E FROM PMSALES WHERE (SONum = @SONum); this.cmdSOID.Connection = this.sqlConnection1; this.cmdSOID.Parameters.Add(new System.Data.SqlClient.SqlParameter(@SONum System.Data.SqlDbType.VarChar 10 SONum)); // // cmdSOUpdate // this.cmdSOUpdate.CommandText = UPDATE PMSALES SET CUSTOMER = @Customer SUBS_QTY = @SUBS_QTY YIELD = @Yield QT + Y = @Qty SHIPDATE = @Shipdate MASTER# = @Master# COMPLETE = @Complete WHERE ( + SONum = @SONum); this.cmdSOUpdate.Connection = this.sqlConnection1; this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Customer System.Data.SqlDbType.VarChar 50 CUSTOMER)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@SUBS_QTY System.Data.SqlDbType.VarChar 10 SUBS_QTY)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Yield System.Data.SqlDbType.VarChar 10 YIELD)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Qty System.Data.SqlDbType.VarChar 10 QTY)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Shipdate System.Data.SqlDbType.DateTime 8 SHIPDATE)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Master# System.Data.SqlDbType.VarChar 10 MASTER#)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Complete System.Data.SqlDbType.VarChar 1 COMPLETE)); this.cmdSOUpdate.Parameters.Add(new System.Data.SqlClient.SqlParameter(@SONum System.Data.SqlDbType.VarChar 10 System.Data.ParameterDirection.Input false ((System.Byte)(0)) ((System.Byte)(0)) SONum System.Data.DataRowVersion.Original null)); // // cmdSOInsert // this.cmdSOInsert.CommandText = INSERT INTO PMSALES (SONum CUSTOMER RUN_TIME PARTNUM QTY) VALUES (@SONum @CU + STOMER @RUN_TIME @PartNum @Qty); this.cmdSOInsert.Connection = this.sqlConnection1; this.cmdSOInsert.Parameters.Add(new System.Data.SqlClient.SqlParameter(@SONum System.Data.SqlDbType.VarChar 10 SONum)); this.cmdSOInsert.Parameters.Add(new System.Data.SqlClient.SqlParameter(@CUSTOMER System.Data.SqlDbType.VarChar 50 CUSTOMER)); this.cmdSOInsert.Parameters.Add(new System.Data.SqlClient.SqlParameter(@RUN_TIME System.Data.SqlDbType.VarChar 10 RUN_TIME)); this.cmdSOInsert.Parameters.Add(new System.Data.SqlClient.SqlParameter(@PartNum System.Data.SqlDbType.VarChar 30 PARTNUM)); this.cmdSOInsert.Parameters.Add(new System.Data.SqlClient.SqlParameter(@Qty System.Data.SqlDbType.VarChar 10 QTY)); this.Load += new System.EventHandler(this.Page_Load); } #endregion public void btnGet_Click(object sender System.EventArgs e) { //Retrieves data based on the Order Number a user //enters in the web form string soNum; soNum = txtSOID.Text; cmdSOID.Parameters[@SONum].Value = soNum; sqlConnection1.Open(); System.Data.SqlClient.SqlDataReader dreader; dreader = cmdSOID.ExecuteReader(CommandBehavior.SingleRow); if (dreader.Read()) { txtCust.Text = dreader[1].ToString(); txtPartNum.Text = dreader[7].ToString(); Qty = dreader[8].ToString(); //Assigns the order quantity to Qty } dreader.Close(); sqlConnection1.Close(); } public void btnSave2_Click(object sender System.EventArgs e) { //Inserts another row with additional data to the table //including the order quantity cmdSOInsert.Parameters[@SONum].Value = txtSOID.Text; cmdSOInsert.Parameters[@Customer].Value = txtCust.Text; cmdSOInsert.Parameters[@RUN_TIME].Value = txtRunTime.Text; cmdSOInsert.Parameters[@PartNum].Value = txtPartNum.Text; cmdSOInsert.Parameters[@Qty].Value = Qty; sqlConnection1.Open(); cmdSOInsert.ExecuteNonQuery(); sqlConnection1.Close(); } } }

tdiddy67 · Answer

Yes but I will have to do it later could you please check back tomorrow? Thanks for the response.

Carlos Sanchez · Answer

Can you post some of your code? If you declare a variable as public you should be able to manipulate in all the methods of the class. e. g. NameSpace MyNameSpace { Public Class MyClass { public string Qty; //Your public variable Public MyMethod1() { Qty = MyString1 } Public MyMethod2() { Qty +=  MyString2 } static void Main() { MyMethod1(); MyMethod2(); Console.Writelin(Qty); //Display MyString1 MyString2 } } }