Explaination for 4.14

[orsenthil]

The program is about macros:
Read this and use the information.
http://en.wikipedia.org/wiki/C_preprocessor#Macro_definition_and_expansion

You can add a reference to the link, like it is done here:

https://raw2.github.com/uthcode/uthcode/chapter2/source/cprogramming/Ex_1.2_exp_printf_c.rst

How to swap two variables in C?

a = 10, b = 20, by using temperory variable t, swap a and b?

t = a;
a = b;
b = t;

print a, b

a = 20, b = 10