To add to what GCDEF said, if you store the unit names and multipliers in an array it is then easy to modify the program to store the conversion data externally, rather than hard-coded within the source code. That is, you store the names and multipliers in a text file which is read in and stored in arrays when the program starts. This would allow the user to add/remove items, or modify the multipliers (in the case of the currency exchange rates) without having to modify the program.