I want to show discount values in textbox

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hello guys in my software I want to show discount values and sum and show in the textbox but I get null values

please help me and tell me how can I do this ?

What I have tried:

C#

DataSet dsa21 = new DataSet();
            DataTable dt21 = new DataTable();
            dsa21.Tables.Add(dt21);
            OleDbDataAdapter da21 = new OleDbDataAdapter();
            da21 = new OleDbDataAdapter("SELECT [Discount] As [Discounts] from [Total] Where [Date] >= #" + dateTimePicker1.Value.ToString("dd/MM/yyyy") + "# AND [Date] < #" + dateTimePicker1.Value.AddDays(1).ToString("dd/MM/yyyy") + "# Group By [Discount]", connection);
            da21.Fill(dt21);
            connection.Close();
            int sum90 = 0;
            for (int i = 0; i < dsa21.Tables[0].Rows.Count; ++i)
            {
                sum90 += Convert.ToInt32(dsa21.Tables[0].Rows[0][0].ToString());
            }
            textBox16.Text = sum90.ToString();

Posted 16-Apr-17 7:23am

Member 9983063

Updated 16-Apr-17 20:12pm

Nirav Prabtani

v3

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[no name] 16-Apr-17 13:32pm

You learn how to use the debugger and find out where the null values are coming from. Then you fix it.

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Patrice T · Answer 1 · 2017-04-16T10:24:00

Never build an SQL query by concatenating with user inputs, it is named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability.
SQL injection - Wikipedia[^]
SQL Injection[^]

Quote:
please help me and tell me how can I do this

First, use the debugger to understanf how you get null values.

When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute, it is an incredible learning tool.

Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.