Prevent alpha character from being entered into a numeric field

[Brazil]

How can I protect a cell so that an alpha character cannot be entered into a
numeric field?

 

[Gary Brown]

Assuming your cursor is in Cell A1:
Use Data Validation.
From the top menu, select...
Data > Validation > Settings > Allow
Select Custom
For 'Formula', put...
=ISNUMBER(A1) = TRUE

 

[M Kan]

Go to the Main Menu: Data: Validation. From there, you can set the
parameters on what can be entered into the cell as well as input and error
messages.

http://www.kan.org/tips/excel_validation.php

 

[Reitanos]

Select Data/Data Validation and select either whole number or decimal
from the list to restrict the cell to that type of content. You get to
set a min and max and can set up an input message (that appears when
the cell is selected - like a comment that responds to selection not
mouse position) and an error message.