conversion between numbers and strings?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello, Perl monks. I'm having a problem with a little program (actually, it's exercise for chapter 10 in the Llama book). Though I understand the book's solution to the excercise, I don't know what's going on with my solution. Here's part of it, which is a sort-of-working script (it runs).

 
$x = int (1 + rand 100);
print "What is the secret random number? ";
while (<STDIN>) { 
    $guess = $_; 

if ($guess eq "quit") { 
    last; 
    } 

elsif ($guess == $x) { 
    print "You got it, brother!\n"; 
    last; 
 } 
elsif ($guess > $x) { 
    print $y;
print "Too high! Try again!\n";

}
elsif ($guess < $x) {
    print "Too low! Try again!\n"; 

 }
}
[download]

What I don't understand is why the "quit" comparison isn't working. When the user types in "quit", the program states that this is "Too low." Is it being converted to zero? I have it using an "eq" operator, so why doesn't it take the input as a string? Shouldn't the program be doing the conversion automatically, depending on the operator? Thanks, Barry

Comment on conversion between numbers and strings? Download Code

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Re: conversion between numbers and strings? by ysth (Canon) on Apr 22, 2004 at 04:24 UTC
When they type quit, they actually type "enter" after the four letters; that becomes part of the string. When the string is converted to a number (for the == compares) the trailing newline (like all whitespace) is silently ignored, but eq is tripped up by it. Traditionally, one handles this by saying: `while (my $guess = <STDIN>) { chomp($guess); ...` [download] See chomp.	[reply] [d/l]
Re: conversion between numbers and strings? by Koosemose (Pilgrim) on Apr 22, 2004 at 04:19 UTC
Your problem is that when things are read from STDIN, it includes the trailing newline, so that if you type quit, $guess ends up being "quit\n" which is, of course, not equal to "quit". The number comparison's work fine, because when it converts to a number any trailing non numerical characters are basically ignored. Just `chomp $guess;` before doing your comparisons Just Another Perl Alchemist	[reply] [d/l]
Re: conversion between numbers and strings? by kvale (Monsignor) on Apr 22, 2004 at 04:20 UTC
When you read in a line, it includes the newline "\n" at the end of the string and thus your string comparison does not work. By contrast, conversion to a number drops the newline, so your numerical comparison does work. To fix it, use chomp: `chomp( $guess = $_);` [download] -Mark	[reply] [d/l]
Re: conversion between numbers and strings? by Anonymous Monk on Apr 22, 2004 at 13:40 UTC
Thank you very much for your quick response! I am at peace. Barry	[reply]