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diff --git a/reference/C/SYNTAX/for.html b/reference/C/SYNTAX/for.html new file mode 100644 index 0000000..e90ac20 --- /dev/null +++ b/reference/C/SYNTAX/for.html @@ -0,0 +1,175 @@ +<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> +<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> |