DataGridViewTextBoxColumn tbCol = new DataGridViewTextBoxColumn(); DataGridViewTextBoxCell tbCell = new DataGridViewTextBoxCell();
// Used for the appearence of the cell, it doesn't mean that there is a correlation between the cell and the column (see below ***)
tbCell.Style.ForeColor = Color.Blue;
tbCol.CellTemplate = tbCell;
tbCol.Name = "qtySelect";
tbCol.HeaderText = "Header";
int colIndex = gridProduct.Columns.Add(tbCol);
const int rowNumber = 0; // define which row you want
//Pay attention that you may need to add rows before writting to the cell
//const int rowNumber = 1;
//gridProduct.Rows.Add();
gridProduct.Rows[rowNumber].Cells[colIndex].Value = "Value for cell";
//*** If you want to work with the cell itself, you first need to get a reference to it
//tbCell = gridProduct.Rows[0].Cells[0] as DataGridViewTextBoxCell;
//tbCell.Value = "1"; // and then you can overwrite the value