Re^2:Example 3: expect the unexpected

One would believe it fails... it doesn't

It tries to do the right thing. The result in general is unpredictable. (That is, for a beginner).
The snippet is:

#! /usr/local/bin/perl

use strict;

sub print_percentage
{
    my ($total, $part) = @_;
    if (int($total) != 0){
        printf ("It's about %.2f%%\n", $part/$total *100.);
    }
    else{
        print "Bad usage: $total == 0!!! Cannot divide by '$total'.\n"
+;
    }

}
    
print_percentage(100, 50);
print_percentage("oops", 50);

;1

One could write many variations on the theme:

#! /usr/local/bin/perl

use strict;

if ("38" == 38){
    print "hit the jackpot!\n";
}
else {
    print "hit elsewhere....\n";
}

;1

Why people do this?

People do mistakes, and they are spoiled by getting used to compilers' help. Many who come to Perl from other languages are used to "it doesn't make any sense" compiler's error. Or run-time exceptions. They are NOT used to the machine "doing the right thing" for them (of course! what do you mean by doing the right thing?) And that's the problem for beginners.

Solution

Set up your mind not to guess what it'll do. Learn, find out, know.