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<html>
<head>
<title>The WHILE keyword.</title>
<script language="JavaScript">
</script>
</head>
<body bgcolor="#ffffcc">
<hr>
<center><h1>The WHILE keyword.</h1></center>
<hr>
The <b>while</b> keyword is related to <a href=do.html>do</a>
and <a href=for.html>for</a>. Its purpose is to repeatedly execute
a <a href="statements.html#blocks">block</a> of statements. Here is
an example :
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
main()
{
int i=5;
while(--i)
{
printf(" i is %d\n", i);
}
}
</pre>
</td>
</tr>
</table>
</center>
<p>
The expression <b>i--</b> is evaluated and if its
<a href="../CONCEPT/true_false.html">true</a> the statements in the
<a href="statements.html#blocks">block</a> are executed.
The loop continues until the expression is false (zero).
The result will look like this:
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
i is 4
i is 3
i is 2
i is 1
</pre>
</td>
</tr>
</table>
</center>
<p>
It is important to note that the statements
on a <b>while</b> will not get executed if the first evaluation of the
expression is FALSE. If you do not want this to happen you may prefer
to use the <a href="do.html">do</a> statement.
<hr>
<p>
Now consider the next example.
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
main()
{
int i=5;
while(--i);
{
printf(" i is %d\n", i);
}
}
</pre>
</td>
</tr>
</table>
</center>
The result will look like this:
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
i is 0
</pre>
</td>
</tr>
</table>
</center>
<p>
This is because of the <b>;</b> on the end of the <b>while</b>
statement which means the <b>while</b> will loop (executing NULL statements)
until <b>i</b> is zero. Execution will then continue down the program
(to the printf).
<p>
<hr>
<h2>Examples:</h2>
<img src="../../GRAPHICS/computer.gif" align=left alt="o">
<a href="../EXAMPLES/while.c">Basic <b>while</b></a>.
<br clear=left>
<hr>
<h2>See also:</h2>
<ul>
<li><a href="while.html">for</a> keyword.
<li><a href="do.html">do</a> keyword.
<li><a href="break.html">break</a> keyword.
<li><a href="continue.html">continue</a> keyword.
</ul>
<p>
<hr>
<p>
<center>
<table border=2 width="80%" bgcolor="ivory">
<tr align=center>
<td width="25%">
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</td>
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</table>
</center>
<p>
<hr>
<address>Martin Leslie
</address><p>
</body>
</html>
|
