If you have been reading the book closely up to this point, you have
seen the use of the printf function many times. To recap, this
function prints a text string to the terminal (or, to be more precise,
the text stream stdout). For example, the following line of code
prints the string Hello there!, followed by a newline character,
to the console:
printf ("Hello there!\n");
You probably also remember that you can incorporate numeric constants and
variables into your strings. Consider the following code example:
The previous example is equivalent to the following one:
int age = 4;
printf ("I'm free! I'm free! (So what? I'm %d.)\n", age);
Both of the code examples above produce the following output:
I'm free! I'm free! (So what? I'm 4.)
You may recall that besides using %d with printf to print
integers, we have also used %f on occasion to print floating-point numbers,
and that on occasion we have used more than one argument. Consider this example:
In fact, printf is a very flexible function. The general scheme
is that you provide it with a format string or template
string (such as "So what? I'm %d."), which can contain zero or
more conversion specifications, conversion specifiers, or
sometimes just conversions (in this case %d), and zero or
more arguments (for example, 4). Each conversion specification is
said to specify a conversion, that is, how to convert its
corresponding argument into a printable string. After the template
string, you supply one argument for each conversion specifier in the
template string. The printf function then prints the template
string, including each argument as converted to a printable sub-string
by its conversion specifier, and returns an integer containing the
number of characters printed, or a negative value if there was an error.
