//to check if some information user put is empty or invalid. bool IsItemDataValid() { //Check if an user input empty information if (ItemNameTxtbox.Text == "" || ItemPriceTxtbox.Text == "" || ItemQuantTxtbox.Text == "") { //Place the focus on the first invalid textbox if (ItemNameTxtbox.Text == "") { ItemNameTxtbox.Focus(); } if (ItemPriceTxtbox.Text == "") { ItemPriceTxtbox.Focus(); } if (ItemQuantTxtbox.Text == "") { ItemQuantTxtbox.Focus(); } return(false); } //Check if the number an user input is negative else if (Convert.ToDecimal(ItemPriceTxtbox.Text) <= 0 || (Convert.ToInt32(ItemQuantTxtbox.Text) <= 0)) { //Place the focus on the first invalid textbox if (ItemPriceTxtbox.Text == "") { ItemPriceTxtbox.Focus(); } if (ItemQuantTxtbox.Text == "") { ItemQuantTxtbox.Focus(); } return(false); } else { return(true); } }