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| author | Tobias Klauser <tklauser@distanz.ch> | 2008-01-27 11:37:44 +0100 |
|---|---|---|
| committer | Tobias Klauser <tklauser@xenon.tklauser.home> | 2008-01-27 11:37:44 +0100 |
| commit | 7e0f021a9aec35fd8e6725e87e3313b101d26f5e (patch) | |
| tree | b1cacc4b24393f517aeb4610e9e1021f954307a8 /reference/C/CONCEPT/constants.html | |
Initial import (2.0.2-6)2.0.2-6
Diffstat (limited to 'reference/C/CONCEPT/constants.html')
| -rw-r--r-- | reference/C/CONCEPT/constants.html | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/reference/C/CONCEPT/constants.html b/reference/C/CONCEPT/constants.html new file mode 100644 index 0000000..e2a7778 --- /dev/null +++ b/reference/C/CONCEPT/constants.html @@ -0,0 +1,143 @@ +<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> +<hr> +<p> +<center> +<table border=2 width=80% bgcolor=ivory> +<tr align=center> +<td width=25%> +<a href="../cref.html">Top</a> +</td><td width=25%> +<a href="../master_index.html">Master Index</a> +</td><td width=25%> +<a href="../SYNTAX/keywords.html">Keywords</a> +</td><td width=25%> +<a href="../FUNCTIONS/funcref.htm">Functions</a> +</td> +</tr> +</table> +</center> +<p> + +<hr> +<address>Martin Leslie +<script language="JavaScript"> +<!-- // +document.write(document.lastModified); +// --> +</script> +</address> |