foreach my $value (@data) {
    $var = 1/($count-1);
    $variance = $var*(($value-$Average)**2);
}

##</code><code>##

for( my $i=0; $i < @data; $i++ ){
  # do something with $data[$i]
}

# or 

for my $i (0..(@data-1)){
  # do something with $data[$i]
}