Graphics Programs Reference
In-Depth Information
statement
b = a / 5
will result in the value of 2 being stored in
b
, since that's
the integer portion of it. Floating-point variables must be used to retain the
more correct answer of 2.6.
Operation
Symbol
Example
Addition
+
b = a + 5
-
b = a - 5
Subtraction
Multiplication
*
b = a * 5
/
b = a / 5
Division
Modulo reduction
%
b = a % 5
To get a program to use these concepts, you must speak its language. The
C language also provides several forms of shorthand for these arithmetic oper-
ations. One of these was mentioned earlier and is used commonly in for loops.
Full Expression
Shorthand
Explanation
i = i + 1
i++ or ++i
Add 1 to the variable.
i = i - 1
i-- or --i
Subtract 1 from the variable.
These shorthand expressions can be combined with other arithmetic
operations to produce more complex expressions. This is where the differ-
ence between
i++
and
++i
becomes apparent. The first expression means
Increment the value of
i
by 1
after
evaluating the arithmetic operation
, while the
second expression means
Increment the value of
i
by 1
before
evaluating the
arithmetic operation
. The following example will help clarify.
int a, b;
a = 5;
b = a++ * 6;
At the end of this set of instructions,
b
will contain 30 and
a
will contain 6,
since the shorthand of
b = a++ * 6;
is equivalent to the following statements:
b = a * 6;
a
= a + 1;
However, if the instruction
b = ++a * 6;
is used, the order of the addition
to
a
changes, resulting in the following equivalent instructions:
a = a + 1;
b
= a * 6;
Since the order has changed, in this case
b
will contain 36, and
a
will still
contain 6.
