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| author | Tobias Klauser <tklauser@distanz.ch> | 2008-01-27 11:37:44 +0100 |
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| committer | Tobias Klauser <tklauser@xenon.tklauser.home> | 2008-01-27 11:37:44 +0100 |
| commit | 7e0f021a9aec35fd8e6725e87e3313b101d26f5e (patch) | |
| tree | b1cacc4b24393f517aeb4610e9e1021f954307a8 /reference/C/SYNTAX/if.html | |
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diff --git a/reference/C/SYNTAX/if.html b/reference/C/SYNTAX/if.html new file mode 100644 index 0000000..8df9bb6 --- /dev/null +++ b/reference/C/SYNTAX/if.html @@ -0,0 +1,133 @@ +<title>if-else keywords.</title> + +<head> +<script language="JavaScript"> +</script> +</head> + +<body bgcolor="#ffffcc"> +<hr> +<center> +<h1>The 'if' and 'else' keywords</h1> +</center> +<hr> +<p> + +The if-else statement is a two-way decision statement. It is written as + +<pre> + if ( expression ) statement1; + [else statement2;] +</pre> + +The else portion is optional. If the expression evaluates to +<a href="../CONCEPT/true_false.html">true</a> +(anything other than 0) then statement1 is executed. If there is an <b>else</b> +statement and the expression evaluates to +<a href="../CONCEPT/true_false.html">false</a> +statement2 is executed. + +For example + +<pre> +(1) + int NumberOfUsers; + . + . + if( NumberOfUsers == 25 ) + { /* No else part */ + printf( "There are already enough users. Try later.\n" ); + return ERROR; + } + . + . + + +(2) if( a >= b ) larger = a; /* else part is present */ + else larger = b; +</pre> + +Consider this code fragment: +<pre> + if( p == 1 ) + if( q == 2 ) r = p * 2 + q; + else r = q * 2 + p; +</pre> +Because the <b>else</b> part is optional, there is an ambiguity when an <b>else</b> is +omitted from a nested if sequence. In 'C', this is resolved by associating +the <b>else</b> with the closest previous if that does not have an <b>else</b>. +Therefore, in the above example, the <b>else</b> part belongs to the if(q==2) +statement. + +The code can be made more readable by explicitly putting parentheses in +the expression, like this + +<pre> + if( p == 1 ) + { + if( q == 2 ) r = p * 2 + q; + } + else r = q * 2 + p; + + OR + + if( p == 1 ) + { + if( q == 2 ) r = p * 2 + q; + else r = q * 2 + p; + } +</pre> + +Because the statement in the <b>else</b> part can also be an if statement, a +construct such as shown below is possible in 'C' to create a multiple +choice construct. + +<pre> + if( expression1 ) + statement1; + else if( expression2 ) + statement2; + else if( expression3 ) + statement3; + . + . + else + statementN; +</pre> + +<hr> +<h2>Example:</h2> +<img src="../../GRAPHICS/computer.gif" align=center> +<a href="../EXAMPLES/if.c"> Basic <b>if</b> example.</a> +<br clear=left> +<hr> +<h2>See also:</h2> +<ul> +<li><a href="switch.html">switch</a> keyword. +</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> |