The variable $price contains all of your input, which includes the new line (Enter). When you print it out as a string in the last line, the new line is printed as well. This doesn't happen later in that line when the price in pounds is printed because you are printing the result of an arithmetic calculation, and the newline is silently dropped (from both $price and $yen) when they are treated as numbers instead of strings ... no they don't cancel out ;-).
There is a command in perl specifically for stripping the Enter key results from your input: chomp. Although it is related to chop, which shmem suggested, it is superior for this purpose because it will work on different platforms (Unix, Windows, Mac OS, etc). chop will not give you what you want in Windows (for example), where the enter key appends two characters.
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