How to Show the Sum of in a Datagridview Column

how I can show the sum of in a datagridview column?

int sum = 0;
for (int i = 0; i < dataGridView1.Rows.Count; ++i)
{
    sum += Convert.ToInt32(dataGridView1.Rows[i].Cells[1].Value);
}
label1.Text = sum.ToString();

Calculate sum of a column in a datagridview c#

In your method, you call the row "row" inside the loop, but declare it as r in the foreach.

I would recommend simplifying your code though. Have a look at the answer here: how I can show the sum of in a datagridview column?

I don't think you need the a & b variables to get at your answer and perhaps you are initializing them differently in the 1st example when you are passing them into the method.

int a= 0;
foreach (DataGridViewRow r in dataGridView1.Rows){
{
    a += Convert.ToInt32(r.Cells[c].Value);
}

DatagridView C# Sum of columns

You could use this query:

var userSums = dataGridView2.Rows.Cast<DataGridViewRow>()
    .GroupBy(row => row.Cells[0].Value.ToString())
    .Select(g => new { User = g.Key, Sum = g.Sum(row => Convert.ToInt32(row.Cells[1].Value)) });

How to get the sum of datagridview columns in C#

It looks like you are not using the correct values for your column names.
For example, this code:

row.Cells[dataGridView1.Columns["Total Test"].Index].Value

Is not going to return a column, since the string "Total Test" is neither a column index or a column name (a column name cannot have spaces). It looks like you are trying to use the column header text. Change it to:

row.Cells[0].Value

(where 0 is the index of the column)

Or:

row.Cells["colTotalTest"].Value

(where colTotalTest is the name of the column)

And do the same for all references to columns.

how I can show the sum of in a datagridview column in asp.net

use table.Compute function

   private void ComputeBySalesSalesID(DataSet dataSet)
{
    // Presumes a DataTable named "Orders" that has a column named "Total."
    DataTable table;
    table = dataSet.Tables["Orders"];

    // Declare an object variable. 
    object sumObject;
    sumObject = table.Compute("Sum(Total)", "EmpID = 5");

    //Find label
     GridViewRow footer = dgOpenBal.FooterRow;
     var lblTotal = (Label)footer.FindControl("lblTotal");
     lblTotal.Text = sumObject.ToString();
}

Another approach use stored procedure to get calculated amount from Sproc

private void ComputeBySalesSalesID(DataSet ds)
{
         if (ds.Tables[0].Rows.Count > 0)
                {
                    DataRow drSum = ds.Tables[0].Rows[0];
                    GridViewRow footer = dgOpenBal.FooterRow;
                    var lblTotal = (Label)footer.FindControl("lblTotal");
                    lblTotal.Text = drSum["sum"].ToString();
                }
}