|
|
C++ tutorial: cout
Use 'cout' for simple output
Probably the simplest form of output that a computer program can produce is to
write plain text onto the screen. That's what 'cout' is for (I pronounce this
like 'c out'; I think it stands for 'console out').
For example, in the programs welcome1.cpp and welcome2.cpp you
should remember the following line:
cout << "Welcome to BIS4221:\n";
'cout <<' is an instruction to write the following thing to the screen.
In this example, the 'thing' to be written is a line of text: "Welcome to BIS4221:\n".
The quotation marks at the start and end of the line indicate that the stuff inside
is to be treated as a single 'lump' of text (technically it is a character array,
of which more later). Everything inside the quotes gets printed to the display,
except the part '\n'. This does not appear in the output. Can you work out what this
does? If you have a C++ compiler, try removing the '\n' and see what happens. If you
don't, the answer is at the bottom of this page.
You can 'cout' several things at once
As you will see, you can use 'cout' to output other types of data, not just
text. You can ouput several things on one line, like this:
cout << something1 << something2;
where the 'somethings' are the data you want to display.
'cout' is an object
Technically, cout is a 'object of class ostream'. An object is a self-contained
entity consisting of functions and data. We will not be introcing objects and
classes until later, but it is as well to get the terminology right at the
beginning. All 'objects of class ostream' are concerned with outputting formatted
data; 'cout' in particular is associated with the display. You can define
related objects to ouput data to files, or to the network. So what does
'<<' mean? One way of interpreting it is as a 'send to' instruction. In other words,
cout << "Welcome to BIS4221:\n";
means 'send a piece of text to the cout object'. Personally I think this is a slightly
ugly notation, as '<<' has another, totally different meaning in C++. One of the
powerful features of C++ is the ability for the programmer to re-define the meaning
of symbols; in this case the designers of C++ thought that '<<' was a good
symbol for 'send to'. I prefer for symbols to mean similar things in all contexts,
as do the designers of Java, as this facility was removed from the Java language.
In any event, '<<' in the context of 'cout' means 'send to'. What do you
think '>>' might mean? All will be revealed in due course!
PS:
'\n' means 'start a new line'. Other similar symbols are available, e.g.,
'\t' means 'indent one tab space'.
|
