read excel data line by line with c# .net

Since Excel works with ranges you should first get the range of cells you would want to read. After that you can now browse through them using a for loop. You can see an example below:

    Excel.Application xlApp = new Excel.Application();
    Excel.Workbook xlWorkbook = xlApp.Workbooks.Open(@"C:\myexcel.xlsx");
    Excel._Worksheet xlWorksheet = xlWorkbook.Sheets[1];
    Excel.Range xlRange = xlWorksheet.UsedRange;

    int rowCount = xlRange.Rows.Count;
    int colCount = xlRange.Columns.Count;

    for (int i = 1; i <= rowCount; i++)
    {
        for (int j = 1; j <= colCount; j++)
        {
            MessageBox.Show(xlRange.Cells[i, j].Value2.ToString());
        }
    }

A more detailed explanation on this code block can be found here.

you can use OleDbDataReader as below

using (OleDbConnection connection = new OleDbConnection(connectionString))
{
    OleDbCommand command = new OleDbCommand(queryString, connection);

    connection.Open();
    OleDbDataReader reader = command.ExecuteReader();

    while (reader.Read())
    {
        var val1= reader[0].ToString();
    }
    reader.Close();
}