You could use IF statements, but it can be clumsy and difficult to support/alter/add to/etc.
Better would be a lookup table.
Given what you have written, you could set up a table like:
Assume that table is in J1:K3
Assume your column data starts in A1.
You could then use the formula:
and fill down as needed. Note that the 99 just needs to be some number longer than the longest total string length of a string in column A