而不是使用for循环，你可以简单地使用 计算 数据表的方法，并通过计算表达式。例如：

  VAR总= double.Parse（yourDataTable.Compute（SUM（列1），）的ToString （））; 
 

另外要格式化的总展示后，小数位2位数字，您可以使用这些选项：

• 的0自定义数字格式字符串：的String.Format（{0：0.00}，计））




• 的定点F格式说明：的String.Format（{0：F2}，计））

I want to show sum of total Price of items. I am facing 2 issues:

• It's showing me wrong total of items price
• I want to add .00 to the total price

You can check issue in the image for a clear explanation.

Here is my code:

tDisplay.Text = "Return/" + "Receipt No:" + Return_Form.setalueforText011;
label1.Text = Return_Form.setalueforText011;

OleDbConnection VCON = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Restaurant.accdb");
DataSet dsa = new DataSet();
DataTable dt = new DataTable();
dsa.Tables.Add(dt);

OleDbDataAdapter da = new OleDbDataAdapter();
da = new OleDbDataAdapter("SELECT [Column1],[Column2],[Column3] from [Total] Where [Receipt No] =  " + label1.Text + "", VCON);
da.Fill(dt);
//dataGridView1.DataSource = dt;

for (int i = 0; i < dt.Rows.Count; i++)
{
    products.Add(new tblProduct() { productName = dt.Rows[i]["Column2"].ToString(),productPrice = Convert.ToDecimal(Math.Round(Convert.ToDecimal(dt.Rows[i]["Column1"].ToString())))});
    label3.Text = dt.Rows[i]["Column3"].ToString();
    textBox59.Text = "Rs: "+String.Format("{0:}", Total);
    tblProduct selected = (tblProduct)(listBox60.SelectedItem);
    Total += (decimal)selected.productPrice;
}
VCON.Close();

Instead of using for loop, You can simply use Compute method of data table and pass an expression to compute. For example:

var total = double.Parse(yourDataTable.Compute("SUM(Column1)", "").ToString());

Also to format total to show 2 digits after decimal place, you can use either of these options:

• The "0" Custom Numeric Format String : string.Format("{0:0.00}", total))

• The Fixed-Point "F" format Specifier: string.Format("{0:F2}", total))