ERROR: Error installing rails: ERROR: Failed to build gem native extension

hi-Im use cygwin and want to install rails (gem install rails)
I have error please help me

$ gem install rails --version 4.2.1
Building native extensions. This could take a while…
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.

/usr/bin/ruby.exe -r ./siteconf20150407-7680-1fo1fpe.rb extconf.rb

checking if the C compiler accepts … *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details.
You may
need configuration options.

Provided configuration options:
–with-opt-dir
–without-opt-dir
–with-opt-include
–without-opt-include=${opt-dir}/include
–with-opt-lib
–without-opt-lib=${opt-dir}/lib
–with-make-prog
–without-make-prog
–srcdir=.
–curdir
–ruby=/usr/bin/ruby
–help
–clean
/usr/share/ruby/2.0.0/mkmf.rb:434:in try_do': The compiler failed to generate a n executable file. (RuntimeError) You have to install development tools first. from /usr/share/ruby/2.0.0/mkmf.rb:549:inblock in try_compile’
from /usr/share/ruby/2.0.0/mkmf.rb:500:in with_werror' from /usr/share/ruby/2.0.0/mkmf.rb:549:intry_compile’
from extconf.rb:80:in nokogiri_try_compile' from extconf.rb:87:inblock in add_cflags’
from /usr/share/ruby/2.0.0/mkmf.rb:599:in with_cflags' from extconf.rb:86:inadd_cflags’
from extconf.rb:337:in `’

extconf failed, exit code 1

Gem files will remain installed in
/home/mohammad/.gem/ruby/gems/nokogiri-1.6.6.
2 for inspection.
Results logged to
/home/mohammad/.gem/ruby/extensions/x86_64-cygwin/nokogiri-1.6
.6.2/gem_make.out

On Tuesday, April 7, 2015 at 7:44:31 AM UTC+2, Ruby-Forum.com User
wrote:

/usr/bin/ruby.exe -r ./siteconf20150407-7680-1fo1fpe.rb extconf.rb
    --without-opt-include=${opt-dir}/include

generate a

extconf failed, exit code 1

Gem files will remain installed in
/home/mohammad/.gem/ruby/gems/nokogiri-1.6.6.
2 for inspection.
Results logged to
/home/mohammad/.gem/ruby/extensions/x86_64-cygwin/nokogiri-1.6
.6.2/gem_make.out

if you haven’t installed DevKit, so do that, it will solve the problem: