# 嵌套循环函数

## nested loops - 语法

Perl中嵌套for循环语句的语法如下-

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

Perl中嵌套while循环语句的语法如下-

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

Perl中嵌套do...while循环语句的语法如下-

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

}while( condition );```

Perl中嵌套直到循环语句的语法如下:

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

Perl中嵌套的foreach循环语句的语法如下-

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

## nested loops - 示例

```#/usr/local/bin/perl

\$a=0;
\$b=0;

# outer while loop
while(\$a < 3) {
\$b=0;
# inner while loop
while( \$b < 3 ) {
print "value of a=\$a, b=\$b\n";
\$b=\$b + 1;
}
\$a=\$a + 1;
print "Value of a=\$a\n\n";
}```

```value of a=0, b=0
value of a=0, b=1
value of a=0, b=2
Value of a=1

value of a=1, b=0
value of a=1, b=1
value of a=1, b=2
Value of a=2

value of a=2, b=0
value of a=2, b=1
value of a=2, b=2
Value of a=3```

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