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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/SYNTAX/glo_int_vars.html | |
Initial import (2.0.2-6)2.0.2-6
Diffstat (limited to 'reference/C/SYNTAX/glo_int_vars.html')
| -rw-r--r-- | reference/C/SYNTAX/glo_int_vars.html | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/reference/C/SYNTAX/glo_int_vars.html b/reference/C/SYNTAX/glo_int_vars.html new file mode 100644 index 0000000..51991c4 --- /dev/null +++ b/reference/C/SYNTAX/glo_int_vars.html @@ -0,0 +1,214 @@ +<title>Global and Local variables declaration.</title> +<head> +<script language="JavaScript"> +</script> +</head> +<body bgcolor="#ffffcc"> +<hr> +<center> +<h1>Global and Local variables.</h1> +</center> +<hr> +<p> + +<h2>Local variables</h2> +Local variables must always be +<a href="../glossary.html#definition">defined</a> +at the top of a block. +<p> +<font color="brown"> +C++ has changed the rules regarding where you can define a +local variable. +<a href=../../CPLUSPLUS/CONCEPT/local_var.html>Click here</a> +for the low down. +</font> +<p> +When a local variable is +<a href="../glossary.html#definition">defined</a> +- it is not initalised by the system, you +must initalise it yourself.<p> +A local variable is +<a href="../glossary.html#definition">defined</a> + inside a <b>block</b> and is only visable +from within the block. +<p> +<center> +<table border=1 width="80%" bgcolor=ivory> +<tr> +<td> +<pre> + + main() + { + int i=4; + i++; + } + +</pre> +</td> +</tr> +</table> +</center> +<p> +When execution of the block starts the variable is +available, and when the block ends the variable 'dies'.<p> +A local variable is visible within nested blocks unless a variable with +the same name is +<a href="../glossary.html#definition">defined</a> + within the nested block. +<p> +<center> +<table border=1 bgcolor=ivory width="80%"> +<tr> +<td> +<pre> + + main() + { + int i=4; + int j=10; + + i++; + + if (j > 0) + { + printf("i is %d\n",i); /* i defined in 'main' can be seen */ + } + + if (j > 0) + { + int i=100; /* 'i' is defined and so local to + * this block */ + printf("i is %d\n",i); + } /* 'i' (value 100) dies here */ + + printf("i is %d\n",i); /* 'i' (value 5) is now visable. */ + } + +</pre> +</td> +</tr> +</table> +</center> +<p> +<a name="global"> +<hr width="50%" align=center> +<h2>Global variables</h2> + +<font color="brown"> +C++ has enhanced the use of +<a href=../../CPLUSPLUS/CONCEPT/scope.html> global variables.</a> +</font> +<p> +Global variables ARE initalised by the system when you +<a href="../glossary.html#definition">define</a> + them! +<p> +<center> +<table border=2 width="50%" bgcolor=ivory> +<tr align=center><td> Data Type </td><td> Initialser </td> </tr> +<tr align=center><td> int </td><td> 0 </td> </tr> +<tr align=center><td> char </td><td> '\0' </td> </tr> +<tr align=center><td> float </td><td> 0 </td> </tr> +<tr align=center><td> pointer </td><td> NULL </td> </tr> + +</table> +</center> +<p> +In the next example <b>i</b> is a global variable, it can be seen and modified by +<b> main </b>and any other functions that may reference it. +<p> +<center> +<table border=1 width="80%" bgcolor=ivory> +<tr> +<td> +<pre> + + int i=4; + + main() + { + i++; + } + +</pre> +</td> +</tr> +</table> +</center> +<p> + +Now, this example has <b>global</b> and <b>Internal</b> variables. +<p> +<center> +<table border=1 width="80%" bgcolor=ivory> +<tr> +<td> +<pre> + + int i=4; /* Global definition */ + + main() + { + i++; /* global variable */ + func + } + + func() + { + int i=10; /* Internal declaration */ + i++; /* Internal variable */ + } + +</pre> +</td> +</tr> +</table> +</center> +<p> + +<b>i</b> in <b>main</b> is global and will be incremented to 5. <b>i</b> in +<b>func</b> is internal and will be incremented to 11. When control returns +to <b>main</b> the internal variable will die and and any reference to +<b>i</b> will +be to the global.<p> + + +static variables can be 'seen' within all functions in this source file. At +link time, the static variables defined here will not be seen by the object +modules that are brought in.<p> +<hr> +<h2>Example:</h2> +<img src="../../GRAPHICS/computer.gif"> +<a href="../EXAMPLES/global.c">An Example program</a>. +<hr> +<h2>See Also:</h2> +See <a href="../CONCEPT/storage_class.html">Storage classes</a> to see the more powerfull +features of variable declarations. + +<p> + +<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="keywords.html"> Keywords</a> +</td><td width="25%"> +<a href="../FUNCTIONS/funcref.htm"> Functions</a> +</td> +</tr> +</table> +</center> +<p> +<hr> +<address>Martin Leslie +</address><p> +</body> +</html> + |