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### Formula program

by perlguru22 (Acolyte)
 on Nov 28, 2012 at 05:19 UTC Need Help??
perlguru22 has asked for the wisdom of the Perl Monks concerning the following question:

I have this following assignment to do. "Write a program that prompts the user for a chemical formula and returns the molecular weight. For example H2O would return 18.01. Use the weights file as your source file for the symbols and their weights. Be sure to include a loop so the user doesn't have to reenter the program to look up a weight. Here's another example: The weight of C12H22O11 (table sugar) is found by looking up the weights of each element and multiplying them by the number of their occurrences and adding them all together. At this level don't worry about parentheses, e.g., Ca(OH)2. However, for an A+ try it after you can calculate weights without parantheses." I've figured out most part of it

Print "enter a formula.\n";
chomp ($form=<STDIN>); @array =$form =~ /[A-Z][a-z]?|\d+/ig

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So if the user inputs H22011C12 it would give me H 22 0 11 C 12 all seperate so my next step is to pass that array into a subroutine. I know I have to multiply the weight of the symbol by the occurrence so if the weight of H is 12.01 I multiply by 22 and so on than I add all the totals I just can't seem to figure out how to start my subroutine I have a weights file goes with this. I was just hoping so one could give me some guidence or explain the process to me Thank you so much.

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Re: Formula program
by mbethke (Hermit) on Nov 28, 2012 at 06:15 UTC

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 [Corion]: Option a) would mean launching cmd.exe /k c:\path\to\ batchfile- launching-perl- script.cmd. Option b) would be to add pause as the last line of said batch file. [LanX]: First day after holidays ... and already stressed by the fact that colleagues changed stuff without communication ... apparently I'm the only one trying to fight entropy [Corion]: LanX: The command is always in the history if you typed it in before. If you didn't type the command into the command line, it will not be there. I think there is doskey which can stuff command lines into the history LanX damns the cult of CB ;-) LanX WTF WTF WTF [LanX]: please forget my last 3 posts [LanX]: Yeah option a doesn't go into history [LanX]: probably I need to teach the app to restart after C-c Kill [Corion]: LanX: Maybe have an infinite-loop cmd file? Much easier than trying to manage that from within Perl IMO [Corion]: Alternatively, relaunch the application from cron (or a Windows cron) every minute

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