G'day piscean,

Welcome to the monastery.

You can do that like this. The tests include one- and two-letter symbols with and without numbers. I'll leave you to replace my rough atomic weights with more precise ones. 

#!/usr/bin/env perl -l

use strict;
use warnings;

my %weight = (C => 12, O => 16, Cl => 35.5); 

my %tests = (
    phenol => ['C6H5OH', 6 * 12 + 1 * 16],
    chloroform => ['CHCl3', 1 * 12 + 3 * 35.5],
);

for my $compound (keys %tests) {
    print '-' x 40;
    print "Compound:   $compound";
    my $formula = $tests{$compound}[0];
    print "Formula:    $formula";
    my $calculated = 0;
    $formula =~ s{([A-Z][a-z]?)(\d*)}{
        exists $weight{$1} and $calculated += $weight{$1} * ($2 || 1)
    }eg;
    print "Expected:   $tests{$compound}[1]";
    print "Calculated: $calculated";
}

[download]

Output:

----------------------------------------
Compound:   phenol
Formula:    C6H5OH
Expected:   88
Calculated: 88
----------------------------------------
Compound:   chloroform
Formula:    CHCl3
Expected:   118.5
Calculated: 118.5

[download]

-- Ken

In reply to Re: How to avoid an alphabet and integer next to it in a string? by kcott
in thread How to avoid an alphabet and integer next to it in a string? by piscean

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.