Perl 循环嵌套

Perl 循环嵌套
Perl 循环

Perl 语言允许在一个循环内使用另一个循环,下面演示几个实例来说明这个概念。
语法
嵌套 for 循环语句的语法:

for ( init; condition; increment ){
   for ( init; condition; increment ){
      statement(s);
   }
   statement(s);
}

嵌套 while 循环语句的语法:

while(condition){
   while(condition){
      statement(s);
   }
   statement(s);
}

嵌套 do…while 循环语句的语法:

do{
   statement(s);
   do{
      statement(s);
   }while( condition );
 
}while( condition );

嵌套 until 循环语句的语法:

until(condition){
   until(condition){
      statement(s);
   }
   statement(s);
}

嵌套 foreach 循环语句的语法:

foreach $a (@listA){
   foreach $b (@listB){
      statement(s);
   }
   statement(s);
}

实例

#!/usr/bin/perl
 
$a = 0;
$b = 0;
 
# 外部循环
while($a < 3){
   $b = 0;
   # 内部循环
   while( $b < 3 ){
      print "a = $a, b = $b\n";
      $b = $b + 1;
   }
   $a = $a + 1;
   print "a = $a\n\n";
}

执行以上程序,输出结果为:

a = 0, b = 0
a = 0, b = 1
a = 0, b = 2
a = 1

a = 1, b = 0
a = 1, b = 1
a = 1, b = 2
a = 2

a = 2, b = 0
a = 2, b = 1
a = 2, b = 2
a = 3

Perl 循环

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