Normally you would write the for loop by hand on the command line to take care of the exact naming convention you want, as a throwaway. Well, you would if the shell were sane, which is pretty much exactly what the Windows/DOS shell is not. In a Unix-style shell this would easily be a one-liner. In bash, I would write:
for i in `seq -w 1 99`; do prog sf${i}.mp sf${i}_dec.mp
No such luck with the Windows shell; the required code is long and complicated enough you wouldn’t want to try doing this without putting in a file first (and I wouldn’t want to try wasting like 30 minutes writing the equivalent script such that it won’t break anything, being that I’m not sitting at a Windows box...). If it were very important that it run on an end user’s computer, that’d be another matter, but if it’s just for you I seriously urge installing something that’s going to make this go down better, such as MSYS (which comes with bash and would be a reasonably gentle introduction to Unix commands, a sort of gateway drug to being a full on command line warrior) or Windows PowerShell (which I personally know nothing about but everyone says it’s way better than the default so I’ll trust them on that one).