I have downloaded the latest version of eclipse and installed it by simply untaring the zip file on my ubuntu edgy machine. I can run eclipse by ./eclipse without any major problems. Then I downloaded the latest version of cdt and untar it, but it automatically goes into eclipse/featyres/ directory which seems to be fine, but when I try to open Window-Open Prespective-Other, I don't see anything related to c/c++.

I tried to install it at first from help-software update, find and install but for some reasons i got error.

I have installed jre and sdk manually on my ubuntu machine and everything is fine with them since tomcat is running without any problem. That's why I don't want to install cdt using synaptics, however I have tried it without any success.

I would be glad if someone helps me

I found where the problem was.
Because I leave my "eclipse" folder so-named on my desktop, I temporarily renamed it so that when I right-click/extract the CDT package, it doesn't error out. Extracting it produces a folder of the same name: eclipse. Then I opened it, copy and pasted the folders from the Features/Plugins folder of the (now named) eclipse folder into the corresponding folders of the (now-named) eclipse_core folder.

In other words, I'm taking all the folders out of the plugins folder of the CDT file, and putting them in the plugins folder of the eclipse (core) file. I do the same for features. Then I launch eclipse. I can see c++ now in the menu