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<title>switch/case keywords</title>
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<h1>The 'switch' and 'case' keywords</h1>
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<hr>
<p>
The <b>switch-case</b> statement is a multi-way decision statement. Unlike the
multiple decision statement that can be created using
<a href=if.html>if-else</a>, the <b>switch</b>
statement evaluates the conditional
<a href="../CONCEPT/expressions.html">expression</a> and tests it against
numerous
<a href="../CONCEPT/constants.html">constant</a>
values. The branch corresponding to the value that the
expression matches is taken during execution.
<p>
The value of the expressions in a switch-case statement must be an ordinal
type i.e.
<a href="../CONCEPT/data_types.html">integer, char, short, long</a>,
etc. Float and double are not
allowed.
<p>
The syntax is :
<p>
<center>
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<td>
<pre>
switch( expression )
{
case constant-expression1: statements1;
[case constant-expression2: statements2;]
[case constant-expression3: statements3;]
[default : statements4;]
}
</pre>
</td>
</tr>
</table>
</center>
<p>
The <b>case</b> statements and the <b>default</b> statement can occur in any
order in
the <b>switch</b> statement. The <b>default</b> clause is an optional clause
that is
matched if none of the constants in the <b>case</b> statements can be matched.
<p>
Consider the example shown below:
<p>
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<tr>
<td>
<pre>
switch( Grade )
{
case 'A' : printf( "Excellent" );
case 'B' : printf( "Good" );
case 'C' : printf( "OK" );
case 'D' : printf( "Mmmmm...." );
case 'F' : printf( "You must do better than this" );
default : printf( "What is your grade anyway?" );
}
</pre>
</td>
</tr>
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<p>
Here, if the Grade is 'A' then the output will be
<p>
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<tr>
<td>
<pre>
Excellent
Good
OK
Mmmmm....
You must do better than this
What is your grade anyway?
</pre>
</td>
</tr>
</table>
</center>
<p>
This is because, in the 'C' <b>switch</b> statement, execution continues on into
the next case clause if it is not explicitly specified that the execution
should exit the <b>switch</b> statement. The correct statement would be:
<p>
<center>
<table bgcolor="ivory">
<tr>
<td>
<pre>
switch( Grade )
{
case 'A' : printf( "Excellent" );
break;
case 'B' : printf( "Good" );
break;
case 'C' : printf( "OK" );
break;
case 'D' : printf( "Mmmmm...." );
break;
case 'F' : printf( "You must do better than this" );
break;
default : printf( "What is your grade anyway?" );
break;
}
</pre>
</td>
</tr>
</table>
</center>
<p>
Although the <b>break</b> in the <b>default</b> clause (or in general, after
the last
clause) is not necessary, it is good programming practice to put it in
anyway.
<p>
An example where it is better to allow the execution to continue into the
next <b>case</b> statement:
<p>
<center>
<table bgcolor="ivory">
<tr>
<td>
<pre>
char Ch;
.
.
switch( Ch )
{
/* Handle lower-case characters */
case 'a' :
case 'b' :
.
.
.
case 'z' :
printf( "%c is a lower-case character.\n", Ch );
printf( "Its upper-case is %c.\n" toupper(Ch) );
break;
/* Handle upper-case characters */
case 'A' :
case 'B' :
.
.
.
case 'Z' :
printf( "%c is a upper-case character.\n", Ch );
printf( "Its lower-case is %c.\n" tolower(Ch) );
break;
/* Handle digits and special characters */
default :
printf( "%c is not in the alphabet.\n", Ch );
break;
}
.
.
</pre>
</td>
</tr>
</table>
</center>
<p>
<hr>
<h2>Example:</h2>
<img src="../../GRAPHICS/computer.gif" align=center>
<a href=../EXAMPLES/switch.c>Basic <b>switch</b> example.</a>
<br clear=left>
<hr>
<h2>See also:</h2>
<ul>
<li><a href=if.html>if keyword</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>
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