A conversion specification begins with a % and consists of up to five
specifiers (most of which are optional). They are (from
left-to-right):
the padding specifier. Note that for floating point numbers, the
minimum width specifier determines the number of characters to the left
of the decimal point.
As mentioned above, it is also possible to include ordinary
characters in the format string that are to be printed literally.
Instead of “20.00”, suppose we would like to print “$20.00”. We can do
so simply by adding a “$” before the argument:

This code will print:
The function takes one, two, or four arguments. (Three arguments will
result in an error.) If only the first argument is used, num is
depicted as an integer with commas separating the thousands: