Hey guys, I've just modified the program. Thank you everyone for helping me and making sure I fully understand how to arrange my commands. Here is it after the modification. Hope anyone leave a comment whether the new program is good or not. Thanks again. 
#!/user/bin/perl -w
use strict;
use warnings;
print "Welcome to the math program\n";
while (1) {
    print "Enter a number\n";
    my $first_number = <STDIN>;
    chomp ($first_number);
    if ($first_number eq 'q') {
        die "Goodbye!\n";
    }
    else {
        print "Enter a second number"; 
        my $second_number = <STDIN>;
        chomp ($second_number);
        my $add;
        my $subtract;
        my $times;
        my $divide;
        if ($second_number !=0) {
            $add = $first_number + $second_number;
            $subtract = $first_number - $second_number;
            $times = $first_number * $second_number;
            $divide = $first_number / $second_number;
            print "$first_number + $second_number =  $add\n";
            print "$first_number - $second_number = $subtract\n";
            print "$first_number x $second_number = $times\n";
            print "$first_number / $second_number = $divide\n";
        }
        else {
            $add = $first_number + $second_number;
            $subtract = $first_number - $second_number;
            $times = $first_number * $second_number;
            print "$first_number + $second_number = $add\n";
            print "$first_number - $second_number = $subtract\n";
            print "$first_number * $second_number = $times\n";
        }
    }
}

[download]

In reply to Re: Homework: simple calculator by R4j4
in thread Homework: simple calculator by R4j4

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.