Inline::CPP annoying warning message

The following Inline::CPP code generates the following annoying warning
message:
    'else if" is wrong syntax, correct if 'elsif'.    Do you want to
continue ?
Does anyone have any ideas on where it's coming from, why and how to get
rid of it ??

use strict;
use warnings;

use Inline 'CPP' => 'DATA';

my( $p, $r, $n, $y ) = ( 600, 50, 2, 3 );
my $rv = interest( $p, $r, $n, $y );
print "\$rv: $rv\n";

__DATA__

__CPP__

double interest( double p, double r, int n, int y )
{
    double  result;
    result = p/ (n*y)  ;
    if ( result == r ) return 0.0 ;
    else if ( result < r )  return -1.0 ;
    else  return result;
}


*My system specifics*

Inline::CPP 0.39

DWIM Perl for Windows (Dwimperl-5.14.2.1-v7-32.exe released on 2012.02.12)
DWIM is a Strawberry Perl for Windows derivative (Strawberry Perl 5.14.2.1
RC ).

OS Windows XP (SP3) (32-bit)

===
*Contents of file   lib\Inline\CPP\Config.pm*

package Inline::CPP::Config;

# Configuration data for CPP.pm; Compiler, libs, iostream filename,
#defines.

use strict;
use warnings;

our $VERSION = '0.38_004';
$VERSION = eval $VERSION; ## no critic (eval)


# DO NOT MANUALLY ALTER THE FOLLOWING TWO LINES: Makefile.PL locates them by
# matching their syntax and identifier names.
our $compiler = 'g++';
our $libs     = '-lstdc++';

# DO NOT MANUALLY ALTER THE FOLLOWING LINE: Makefile.PL locates it by
# matching its syntax and identifier name.
our $iostream_fn = 'iostream';



# DON'T EDIT THIS HERE-DOC.  These are set by Makefile.PL.  Override
# by supplying undefs in an AUTO_INCLUDE configuration.
our $cpp_flavor_defs =  <<'END_FLAVOR_DEFINITIONS';

#define __INLINE_CPP_STANDARD_HEADERS 1
#define __INLINE_CPP_NAMESPACE_STD 1

END_FLAVOR_DEFINITIONS

1;

__END__

=head1  Inline::CPP::Config

For internal consumption; nothing to document.