?? perl 語言－perl 中文教程（第七章）.htm
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class=myFont><SPAN class=myFont><FONT face=宋體>翻譯：</FONT></SPAN></SPAN>
<SPAN class=myFont><SPAN class=myFont>flamephoenix</SPAN></SPAN> <BR>
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<P align=center><B>第七章 控制結構</B></P>
<P><A
href="http://www.sun126.com/perl5/perl5-7.htm#一、條件判斷">一、條件判斷</A><BR><A
href="http://www.sun126.com/perl5/perl5-7.htm#二、循環：">二、循環：</A><BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#1、while循環">1、while循環</A>
<BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#2、until循環">2、until循環</A>
<BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#3、類C的for循環">3、for循環</A>
<BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#4、針對列表(數組)每個元素的循環">4、針對列表(數組)每個元素的foreach循環</A><BR>
<A
href="http://www.sun126.com/perl5/perl5-7.htm#5、do循環">5、do循環</A><BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#6、循環控制">6、循環控制</A>
<BR> <A
href="http://www.sun126.com/perl5/perl5-7.htm#7、傳統的goto label;語句。">7、傳統的goto語句</A><BR><A
href="http://www.sun126.com/perl5/perl5-7.htm#三、單行條件">三、單行條件</A><BR><BR><A
name=一、條件判斷>一、條件判斷</A> <BR> if ( <expression>)
{<BR> <statement_block_1><BR> }<BR> elsif
( <expression> )
{<BR> <statement_block_2><BR> }<BR> ...<BR> else{<BR> <statement_block_3><BR> }<BR><BR><A
name=二、循環：>二、循環：</A> <BR><A name=1、while循環>1、while循環</A>
<BR> while ( <expression> )
{<BR> <statement_block><BR> }<BR><A
name=2、until循環>2、until循環</A> <BR> until ( <expression> )
{<BR> <statement_block><BR> }<BR><A
name=3、類C的for循環>3、類C的for循環</A> ，如<BR> for ($count=1; $count
<= 5; $count++) {<BR> # statements inside the
loop go here<BR> }<BR>下面是在for循環中使用逗號操作符的例子：<BR> for
($line = <STDIN>, $count = 1; $count <= 3; $line =
<STDIN>, $count++) {<BR> print
($line);<BR> }<BR>它等價于下列語句：<BR> $line =
<STDIN>;<BR> $count = 1;<BR> while ($count
<= 3) { <BR> print
($line);<BR> $line =
<STDIN>;<BR> $count++;<BR> }<BR><A
name=4、針對列表(數組)每個元素的循環>4、針對列表(數組)每個元素的循環：foreach，語法為：</A><BR> foreach
localvar (listexpr)
{<BR> statement_block;<BR> }<BR>例：<BR> foreach
$word (@words) {<BR> if ($word eq "the")
{<BR> print ("found the word 'the'\n");
<BR> }<BR> }<BR>注：<BR>(1)此處的循環變量localvar是個局部變量，如果在此之前它已有值，則循環后仍恢復該值。<BR>(2)在循環中改變局部變量，相應的數組變量也會改變，如：<BR> @list
= (1, 2, 3, 4, 5);<BR> foreach $temp (@list)
{<BR> if ($temp == 2)
{<BR> $temp =
20;<BR> }<BR> }<BR>此時@list已變成了(1, 20, 3,
4, 5)。<BR><A name=5、do循環>5、do循環</A> <BR> do
{<BR> statement_block<BR> }
while_or_until (condexpr);<BR> do循環至少執行一次循環。<BR><A
name=6、循環控制>6、循環控制</A>
<BR> 退出循環為last，與C中的break作用相同；執行下一個循環為next，與C中的continue作用相同；PERL特有的一個命令是redo，其含義是重復此次循環，即循環變量不變，回到循環起始點，但要注意，redo命令在do循環中不起作用。<BR><A
name="7、傳統的goto label;語句。">7、傳統的goto label;語句。</A> <BR><BR><A
name=三、單行條件>三、單行條件</A> <BR> 語法為statement keyword
condexpr。其中keyword可為if、unless、while或until，如：<BR> print
("This is zero.\n") if ($var == 0);<BR> print
("This is zero.\n") unless ($var != 0);<BR> print
("Not zero yet.\n") while ($var-- >
0);<BR> print ("Not zero yet.\n") until ($var-- ==
0);<BR> 雖然條件判斷寫在后面，但卻是先執行的。</P></TD></TR></TBODY></TABLE>
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