Microsoft Office Tutorials and References
In Depth Information
Megaformula Examples
The example in this section describes a megaformula that determines whether a credit card
number is a valid number.
The basic formulas
Figure 20-6 shows a worksheet set up to analyze a credit card number and determine its validity.
This workbook uses quite a few formulas to make the determination.
Figure 20-6: The formulas in this worksheet determine the validity of a credit card number.
You can access the credit card number validation workbook on the companion
CD-ROM. The file is named credit card validation.xlsx .
In this worksheet, the credit card number is entered in cell F1, with no spaces or hyphens. The
formula in cell F2 follows. This formula appends leading zeros, if necessary, to make the card
number exactly 16 digits long. The other formulas use the string in cell F2.
=REPT(“0”,16–LEN(F1))&F1
When entering a credit card number that contains more than 15 digits, you must be
careful that Excel does not round the number to 15 digits. You can precede the number
with an apostrophe or preformat the cell as Text (using Home➜Number➜Number
Format➜Text).
 
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