C program under Linux

I have recently(yesterday) started trying to learn linux and to program in this os. Now, one interesting and probably easy problem I came across while surfing the net was something like this:

Consider a C program that takes a directory as an argument in the command line and calculates the sum of all the files’ dimensions that are in the directory’s tree.

Now, due to the fact that I’ve been doing a lot of reading and researching in a short matter of time, all my knowledge is piled up in my brian creating a cloud of confusion. If anyone could help me with the code, I’d be really thankful.