Perl 循环嵌套

Perl 循环 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 Perl 循环

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