Following on from adrianh, also consider...

print "==" if $a == ($b * $c);
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and of course, the potential confusion with..

$a = "2.0";
print "eq" if $a eq "2"; # Nope
print "==" if $a == 2;   # Yup
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Basically, not all equality comparisons are string-based. In my 'perl mindset', if $a == "2", where the number is quoted, immediately begs the question as to which type of comparison is wanted...
if $a eq "2" suggests that $a *generally* holds a non-numeric string...maybe part of something like foreach my $a (split(/\s+/,"my 1 markup 2 scheme where numbers 3 do 2 stuff")),whereas if $a == 2 suggests that $a *always* holds a number (and use warnings will then tell me if it doesn't for any reason).

Cheers, Ben