If one cell contains #, & other cell is blank, show message & require blank be resolved

Thank you in advance to any help that comes my way. I am trying to figure out how to make the following happen:

If B5:B6 contains numbers, and C5 is blank, then show messagebox that says "You must select a code for your time."
If B7:B8 contains numbers, and C7 is blank, then show messagebox that says "You must select a code for your time."
If B9:B10 contains numbers, and C9 is blank, then show messagebox that says "You must select a code for your time."
If B11:B12 contains numbers, and C11 is blank, then show messagebox that says "You must select a code for your time."
If B13:B14 contains numbers, and C13 is blank, then show messagebox that says "You must select a code for your time."

If C5:C13 contains any information, and B16 is blank, then show messagebox that says "You have coded a day with no scheduled hours. Please enter the number of hours you were scheduled for the day you have coded."