Expression between datatable values using C#

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Hi , i want to declare mathematical expression between values from datatable , for example: i have two columns named 'Variable'(string) and 'Contents' (float) , i have inserted in 'Variables' 3 string a , b and c and in 'Contents' 3 floats are 0, 3 and 6 .Now i want to declare 'a=b+c' in code an when i click on a 'button' the variable a will change in datatable to 9. here is my code but it doesn't work!! help me please !

What I have tried:

C#

private void button11_Click(object sender, EventArgs e)
        {
            con.Open();
            SqlCommand cmd = con.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "select * from TableVar ";
            cmd.ExecuteNonQuery();
            DataTable dt = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(dt);
            DataRow dr1 = dt.Select("Variable='a'").FirstOrDefault();
            DataRow dr2 = dt.Select("Variable='b'").FirstOrDefault();
            DataRow dr3 = dt.Select("Variable='c'").FirstOrDefault();
             
                dr1["Contents"] = Convert.ToDouble(dr2["Contents"])+ Convert.ToDouble(dr3["Contents"]);
                con.Close();
        }

Posted 22-Nov-19 3:17am

foreigh

Updated 27-Nov-19 10:30am

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Comments

Leo Chapiro 22-Nov-19 10:05am

Try to debug your code row by row.

foreigh 22-Nov-19 10:09am

but i have 3 drows how can i do that ?

#realJSOP 22-Nov-19 10:26am

with the debugger.

foreigh 22-Nov-19 10:34am

can you please show me how for example i'm newb ! please

#realJSOP 22-Nov-19 10:48am

google "how to use visual studio debugger". It's highly likely you'll find a video on youtube.

foreigh 22-Nov-19 13:01pm

i tried but still didn't understand why my code doesn't work

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Maciej Los · Answer 1 · 2019-11-27T10:30:00

You can achieve that using 2 methods:
1) DataTable.Compute(String, String) Method (System.Data) | Microsoft Docs[^]

C#

DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[]
	{
		new DataColumn("Variable", typeof(string)),
		new DataColumn("Contents", typeof(int))
	});
dt.Rows.Add(new object[]{"a", 0});
dt.Rows.Add(new object[]{"b", 3});
dt.Rows.Add(new object[]{"c", 6});

var sumObject = dt.Compute("Sum(Contents)", "Variable IN ('a', 'b', 'c')");
//returns: 9

2) Enumerable.Sum Method (System.Linq) | Microsoft Docs[^]

C#

string[] tofind = {"a", "b", "c"};
var result = dt.AsEnumerable()
	.Where(x => tofind.Any(y=> (x.Field<string>("Variable").Equals(y))))
	.Sum(x=>x.Field<int>("Contents"));
//returns: 9

You might be interested in reading this excellent article: A Calculation Engine for .NET[^]