How do I make one cell blank if another cell has data in it and vice-versa?

[Nosilla]

Hi,

I'm new to the forum today so, first off, hello! I'm hopeful that someone here can help me sort a small issue that I feel like i should be able to solve but for some reason i have not found a good solution so far.

I have created a resource request form in Excel 2010 and on it I need the requestor completing the form to specify how long they are requesting the resource for. To do this they can either enter the duration they will need the resource for as a total number of days or they can specify an end date. I would ideally like a macro that restricts the user so they can only enter data into one or other of the two cells (End date = C15, Duration = C16). If they try and enter data into both cells then the data is only kept in the last cell updated.
e.g.
If C15 contains an end date and the duration in C16 is left blank, this is fine. However, if they then try and enter a duration in C16 without deleting the end date in C15 then C15 would be made blank and vice versa.

I hope this description is clear and one of you can help me to get this to work.

Thanks

[ragulduy]

Maybe use data validation, for example, for the data validation (choose custom) in C15 put something like:
=IF(C16<>"",0,"<>"&0)
and then likewise in C15

[Nosilla]

Thanks Yudlugar, this is not quite what I envisaged initially but it works a treat all the same.