I have some idea but i am puzzled.
As i understand, file inclusion problems like x includes y and y in turn includes x etc. can be avoided by #ifdef preprocessor checks.
Can you please explain with detailed examples on scenarios which result in Multiple File Inclusion problems?

The best way i employ is :
Let us say we have 4 files:
x.h y.h
x.c y.c

x.h includes y.h.
Now...