Consider having three
methods: one to to the F->C conversion, one to do the cm->" conversion, and main() as the third method.
main() would be quite simple. It would prompt the user and then read what they enter. It would use an if-statement to decide which of the other two methods it would call.
Packaging separate functionality into separate methods like this helps to give your program some structure.
When you post code don't include line numbers as people often copy and paste the code in order to compile it and see it run. But do
use the "code" tags. The iea is that you put [code] at the start of a section of code and [/code] at the end. That way the forum software will format the code properly with indents and things and people will be able to read it easily.
--- Update ---
Double post. (@OP: don't do this.) I'll merge with the other thread.