In Excel you can use:
- data validation, with a list of permitted values. In this case a drop-down arrow appears when the cell is active. It is possible to add entry and error messages,
- forms dropdown, with a list in range and linked cell as target.
In both cases value selected appears in the cell.
In the first case user can still clear cell contents or paste value not in list.
In the second case user can write any value in linked cell.
combo