Stop Excel being closed if criteria not completed

[coach.32]

I am trying to figure out how to stop Excel from being closed by an operative if they haven't populated all obligatory cells.
I am trying to stop the person from closing the workbook until they have completed cell C4 with a Yes or No.
I assume that VBA is the way to go but I am not very good a writing it. I keep thinking If A4 > "", then a message comes up requesting that a Yes or No be placed in C4 before closing the workbook.
I want the code to cover the whole of the columns, as different people use it and some do forget to include the required Yes or No.
Of course, this sample is simplified.
Would somebody be so kind as to give me a hand please?

[ferday]

i had this one in my saved notes, i've used it before. you'll just need to adjust the requirements to fit your own purpose of course

[Logit]

Paste this macro in ThisWorkbook module :

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[coach.32]

Thank you so much every one. Life savers.

[Logit]

You are welcome