+print "INPUT 1st NUMBER > ";
+my $first_num = <STDIN>;
+print "INPUT 2nd NUMBER > ";
+my $second_num = <STDIN>;
+# 書き方は色々ある・・・けど、わかりやすい書き方を意識する
+# 文字列と計算結果(数字)を分けるとわかりやすいのではないか
+print "$first_num + $second_num = " . ( $first_num + $second_num ) . "\n";
+print "$first_num - $second_num = " . ( $first_num - $second_num ) . "\n";
+print "$first_num * $second_num = " . ( $first_num * $second_num ) . "\n";
+print "$first_num / $second_num = " . ( $first_num / $second_num ) . "\n";