sub tostring {
my $cent = "00". shift;
$cent =~ s/(\d\d)$/.$1/;
$cent =~ s/^0+(\d)/$1/;
1 while($cent =~ s/(\d)(\d\d\d[.'])/$1'$2/);
$cent;
}

print tostring(2)." + ".tostring(99998)." = ".tostring(100000)."\n";
# => .02+999.98=1'000.00
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