c++ - last two problems with app (i think)

[BabaG]

this post describes my project:

http://www.cplusplus.com/forum/beginner/2058/

i've got most of the project completed now and need help on the
(hopefully) last two obstacles. they are:

1. how to run a command line app from within my app
2. how to tell my app to:

do {
   a bunch of things here
while (there are still files in the directory)
}

my app is for processing lots of photos with a command line
app called nconvert. i need to know how i execute nconvert
with its parameters from within my c++ app. an example of
an nconvert command might be:

nconvert -o tga -crop 100 100 input_filename output_filename

i have a directory filled with photos. it's one of three
directories i use for processing. they are:

receiving
done_orig
done_processed

i will run my c++ app on the receiving directory. as each
file is processed, i moved the original out to the done_orig
directory and the new processed photo out to the done_processed
directory. that way the c++ app should end when there are no
more photos left in the receiving directory and this is why i
need to figure out the coding of the do...while loop above.

thanks for any help,
BabaG