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<title>The FOR keyword.</title>
<head>
<script language="JavaScript">
</script>
</head>
<body bgcolor="#ffffcc">
<hr>
<center><h1>The FOR keyword.</h1></center>
<hr>
The <b>for</b> <a href="../glossary.html#keyword">keyword</a> is used to
repeat a block of code many times.
<p>
<ul>
<li><a href=#basic>Basic principles.</a>
<li><a href=#repeat>Repeating several lines of code</a>
<li><a href=#detail>More detail</a>
</ul>
<a name=basic>
<hr>
<h2>Basic principles</h2>
Say you wanted to print all the numbers between 1 and 10, you could write:
<pre>
main()
{
int count=1;
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
printf("%d\n", count++);
}
</pre>
As you can see this program would NOT be very practical if we wanted
1000 numbers. The problem can be solved with the <b>for</b> statement
as below.
<pre>
main()
{
int count;
for ( count=1 ; count <= 10 ; count++) printf("%d\n", count);
}
</pre>
The <b>for</b> statement can be broken down into 4 sections:
<p>
<dl>
<dt><samp>count=1</samp>
<dd>is the initalisation.<p>
<dt><samp>count <= 10 </samp>
<dd>An expression. The for statement continues to loop while this
statement remains <a href="../CONCEPT/true_false.html">true</a><p>
<dt><samp>count++ </samp>
<dd><a href="../CONCEPT/inc_dec.html">increament</a> or
<a href="../CONCEPT/inc_dec.html">decreament</a>.<p>
<dt><samp>printf("%d\n", count) </samp>
<dd>the statement to execute.<p>
</dl>
<a name=repeat>
<hr>
<h2>Repeating several lines of code</h2>
The previous example showed how to repeat ONE statement. This example
shows how many lines can be repeated.
<pre>
main()
{
int count, sqr;
for ( count=1 ; count <= 10 ; count++)
{
sqr=count * count;
printf( " The square of");
printf( " %2d", count);
printf( " is %3d\n", sqr);
}
}
</pre>
The <b>{</b> and <b>}</b> following the <b>for</b> statement define
a <a href=statements.html#block>block</a> of statements.
<a name=detail>
<hr>
<h2>More detail</h2>
The <b>for</b> statement performs the following functions while looping.
<pre>
for (expression_1 ; expression_2 ; expression_3) statement ;
</pre>
<ol>
<li>Executes <samp>expression_1</samp>.<p>
<li>Executes <samp>statement</samp>.
<li>Executes <samp>expression_3</samp>.
<li>Evaluates <samp>expression_2</samp>.
<p>
<ul>
<li>If TRUE, Jumps to item 2.
<li>If FALSE, Stops looping.
</ul>
</ol>
Any of the three expressions can be missing, if the first or third is missing,
it is ignored. If the second is missing, is is assumed to be TRUE.<p>
The following example is an infinite loop:
<pre>
main()
{
for( ; ; ) puts(" Linux rules!");
}
</pre>
<hr>
<h2>Examples:</h2>
<a href=../EXAMPLES/for1.c><img src="../../GRAPHICS/computer.gif" align=left></a>
Basic <b>for</b> example.
<br clear=left>
<a href=../EXAMPLES/for2.c><img src="../../GRAPHICS/computer.gif" align=left></a>
Advanced <b>for</b> example.
<br clear=left>
<hr>
<h2>See also:</h2>
<ul>
<li><a href="while.html">while</a> keyword.
<li><a href="do.html">do</a> keyword.
<li><a href="continue.html">continue</a> keyword.
<li><a href="break.html">break</a> keyword.
<li><a href="got_ya.html#num1">for got_ya</a>.
</ul>
<p>
<hr>
<p>
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<p>
<hr>
<address>Martin Leslie
</address><p>
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