why does the following recursive directory creation fail?

i have posted this same question on stackoverflow and i got as far as shown. But still i have some errors(synactical and logical) which i couldn’t solve at all.
May be i can get some help here;

i expect to have more than one million files with unique names. I have been told that if i put all this files in one or two directories the search speed for these files will be extremely slow. So i have come up with the following directory architecture.

I want the directory structure to branch out with 10 sub directories and the level of the sub directories will be 4. because the file names are guaranteed to be unique i want to use these file names to make hashes which can be used to put the file in a directory and also later to find it. The random hash values will make a directory to have,approximately, 1,000 files.

so if F is root directory then inserting or searching for a file will have to go through these steps:

I want to use numbers from 0-9 as directory names

h=hash(filename)
sprintf(filepath,“f//%d//%d//%d//%d//.txt”,h,h,h,h);
HOW DO I CREATE THESE DIRECTORIES?

EDIT:

All the files are text files. The program will be distributed to many people in order to collect information for a research. So tt is important that these files are created like this.