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<title>Constants</title>
<body bgcolor="#ffffcc">
<hr>
<center><h1>Constants</h1></center>
<hr>
Be sure you understand the difference between a 'constant' and a
<a href=../glossary.html#declaration>declaration</a>.
A constant has a value that cannot be changed. For example:
<pre>
1234
'x'
9.89
"String"
</pre>
Constants are used to assign a value to a variable. E.G
<pre>
int i; /* declare a variable called 'i' */
i=1234; /* assign the constant value 1234 to
* the variable 'i' */
i++; /* Change the value of the variable. */
</pre>
<ul>
<li><a href="#int">Integer constants.</a>
<li><a href="#float">Floating point constants.</a>
<li><a href="#char">Character constants.</a>
<li><a href="#str">String constants.</a>
</ul>
<hr>
<h2><a name=int>Integer constants.</h2>
Interger constants can be expressed in the following ways.
<pre>
1234 (decimal)
0xff (Hexidecimal)
0100 (Octal)
'\xf' (Hex character)
</pre>
Examples of their use are:
<pre>
int i=255; /* i assigned the decimal value of 255 */
i-=0xff /* subtract 255 from i */
i+=010 /* Add Octal 10 (decimal 8) */
/* Print 15 - there are easier ways... */
printf ("%i \n", '\xf');
</pre>
Integer constants are assumed to have a datatype of
<a href=data_types.html#int> int</a>, if it will not fit into an 'int'
the compiler will assume the constant is a
<a href=data_types.html#modifier>long</a>. You may also force the
compiler to use 'long' by putting an 'L' on the end of the
integer constant.
<pre>
1234L /* Long int constant (4 bytes) */
</pre>
The other modifier is 'U' for Unsigned.
<pre>
1234U /* Unsigned int */
</pre>
and to complete the picture you can specify 'UL'
<pre>
1234UL /* Unsigned long int */
</pre>
<hr>
<h2><a name=float>Floating point constants.</h2>
Floating point constants contain a decimal point or exponent. By default
they are <a href=data_types.html#double>double</a>.
<pre>
123.4
1e-2
<hr>
</pre>
<h2><a name=char>Chararacter constants.</h2>
Are actually integers.
<pre>
'x'
'\000'
'\xhh'
<a href=../FUNCTIONS/escape.html>escape sequences</a>
</pre>
<hr>
</pre>
<h2><a name=str>String constants.</h2>
Strings do not have a <a href=data_types.html>datatype</a> of their own.
They are actually a sequence of char items terminated with a
<a href=../SYNTAX/null.html>\0</a>. A string can be accessed with a
<b>char</b> pointer.
<p>
An example of a string would be:
<pre>
char *Str = "String Constant";
</pre>
See the discussion on <a href=../CONCEPT/string.html>
strings</a> for more information.
<p>
<hr>
<h2>Also see:</h2>
<ul>
<li><a href=../SYNTAX/define_preprocessor.html>#define</a>
<li><a href=../CONCEPT/string.html>Strings</a>
</ul>
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<address>Martin Leslie
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