A nested loop is just one loop within another. The most common use of this is to read from or write into a multi-dimensional array.
Example (in C-style pseudocode):
int[][] array = some...
C, C#, Java, and C++ using two forms: post-increment, x++; pre-increment: ++x; replace increment with decrement: x-- and --x Essentially, they are short hands for x = x + 1; or x = x - 1, or x +=1; x...