Training, Open Source computer languages
PerlPHPPythonMySQLApache / TomcatTclRubyJavaC and C++LinuxCSS 
Search for:
Home Accessibility Courses Diary The Mouth Forum Resources Site Map About Us Contact
Python, Lua and Tcl - public course schedule [here]
Private courses on your site - see [here]
Please ask about maintenance training for Perl, PHP, Java, C, C++, Ruby, MySQL and Linux / Tomcat systems
Do something at least once!

Posted by admin (Graham Ellis), 1 December 2002
While and for loops can be skipped over completely if the initial conditions is false when the loop is entered from above, until loops can be skipped over if the initial condition is true, and foreach loops can be skipped over if you run them on an empty list.

So if you want to force a loop to perform at least once (for example, if you want to prompt and read an answer at least once,  and keep prompting until the user enters a valid respone)  how do you do it?   One way is simply to program carefully so that your while loop  always enters with a true condition, but Perl also provides a do ... while loop that will check the condition after running the code in the block rather than before.

Here's an example of do ... while prompring for an input, and then reprompring as many times as necessary until the user enters just a single word response.

sub getplayer {
       $angle = $_[0];
       do {
       $rpt = 0;
       print "Player sitting at $angle is ... ";
       chomp ($response = <STDIN>);
       ($response !~ /^\S+$/) and
                       print "One name please\n" and
               while ($rpt);
       return ($response);

This page is a thread posted to the opentalk forum at and archived here for reference. To jump to the archive index please follow this link.

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2018: Well House Manor • 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01225 708225 • FAX: 01225 793803 • EMAIL: • WEB: • SKYPE: wellho