|
In
C++ a statement controls the sequence of execution,
evaluates an expression, or does nothing (the null
statement). All C++ statements end with a semicolon,
even the null statement, which is just the semicolon
and nothing else. One of the most common statements
is the following assignment statement:
x
= a + b;
Unlike
in algebra, this statement does not mean that x
equals a+b. This is read, "Assign the value of the
sum of a and b to x," or "Assign to x, a+b." Even
though this statement is doing two things, it is
one statement and thus has one semicolon. The assignment
operator assigns whatever is on the right side of
the equal sign to whatever is on the left side.
New Term: A null statement is
a statement that does nothing.
Whitespace
Whitespace
(tabs, spaces, and newlines) is generally ignored
in statements. The assignment statement previously
discussed could be written as
x=a
+ b;
or as
x=a
+ b;
Although
this last variation is perfectly legal, it is
also perfectly foolish. Whitespace can be used
to make your programs more readable and easier
to maintain, or it can be used to create horrific
and indecipherable code. In this, as in all things,
C++ provides the power; you supply the judgment.
New Term: Whitespace characters
(spaces, tabs, and newlines) cannot be seen. If
these characters are printed, you see only the
white of the paper.
Blocks
and Compound Statements
Any
place you can put a single statement, you can
put a compound statement, also called a block.
A block begins with an opening brace ({) and ends
with a closing brace (}). Although every statement
in the block must end with a semicolon, the block
itself does not end with a semicolon. For example
{
temp
= a;
a
= b;
b
= temp;
}
This
block of code acts as one statement and swaps
the values in the variables a and b.
DO
use a closing brace any time you have an opening
brace. DO end your statements with a semicolon.
DO use whitespace judiciously to make your
code clearer.
|