Please note that "Illegal division by zero" is not a warning but an exception, i.e. a fatal error. With a warning, the script will usually print the warning and continue to execute. Not so with "Illegal division by zero": the program will immediately cease to execute (unless you trap the exception). Consider this one-liner:

$ perl -e 'use strict; use warnings; my $c = 1/0; print "we get there\
+n";'
Illegal division by zero at -e line 1.

$
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As you can see, the final statement is not executed, we don't even "get there".

Compare to this, where the error is trapped within an eval block:

$  perl -e 'use strict; use warnings; eval {my $c = 1/0;};  print "we 
+get there but got the following problem:\n $@ \n";'
we get there but got the following problem:
 Illegal division by zero at -e line 1.

$
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Here, the program does not die, but checking the value of the $@ makes it possible for the developer to possibly take other actions than just dying (for example if something can be recovered, so that the error should not be fatal).