|You could probably use the VLOOKUP() function with some type of table of conversions and get what your looking for.|
With your sheet looking like this, with your Conversion Table in Columns D & E
A B C D E
1) C 3 A 1
2) b 2 B 2
3) E 5 C 3
4) D 4
5) E 5
In Cell B1 enter the formula:
Drag down as many rows as needed.
Then when you enter a letter in Column A, the formula
looks up the corresponding code in your table array
and returns the associated number.
See how that works for you.