I hope you're not trying to use "1 X 10³" as a numeric literal in your code, since that's nowhere near correct.
If you're using that in a string (e.g. as a prompt to the user) it's not a problem. If you want to use scientific notation to specify a value for a float or double, the proper syntax is 1e3. Also, in this way, 1x10^(-3) would be 1e-3. The "e" means "times 10 to the power of."