C++ tutorial: comments
Statements tell the computer what to do
As far as the computer is concerned, the program consists of a number of
statments. A statement is an instruction to do something. Some statements
will correspond to simple actions in the computer, like adding two numbers
together, while some will produce very complicated actions. Statements have a
semicolon (;) at the end, to indicate to the compiler that this is the end
of the statement. The compiler will be very fussy about semicolons, and many
beginners find it hard to remember where they go. Practise will sort this out.
Comments tell people what the computer is to do
Because the language statements are so terse, it is customary to add comments to
the program for the benefit of human readers. The comments will be ignored by the
compiler, and therefore will not be part of the final program that the computer
executes. Comments can be as long or short as you like. In my opinion, the
program itself is not the place for extensive description; there is a place
for this, in the design documentation. However, this is largely a matter of taste.
At the very least, I would recommend a brief comment at the start of the program
file saying what it is for and who wrote it.
A simple program: 'welcome.cpp'
Click here to look at this very simple program. When you have examined it, use your
Web browser's 'back' function to get back to here.
'welcome.cpp' when executed simply displays the following message:
Welcome to BIS4221:
software engineering and management.
The first part of the program is a comment block saying what the program does,
who wrote it, and when.
/*==============================================================================
Program: Welcome
File: welcome.cpp
Author: Kevin Boone
Purpose: 1. to display a simple message
2. to demonstrate the structure of a simple C program
3. to give students practise in downloading and compiling files
History:
Created 5/12/97
================================================================================*/
This part is not meaningful to the computer, it simply tells the reader what's
going on. The fact that this is a comment is signalled by the use of the symbols
'/*' (start of comment) and '*/' (end of comment).
Another way of introducing a comment is the symbol '//'. This means 'the rest of the
line is a comment'. You can put anything you like after '//' and the computer
will ignore it.
Everything else in the program is a statement, that is, an instruction to do
something.
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