how to know which software is installed from source
 

if we install software from rpm we can check using rpm command(rpm -qa | grep -i package),what about if we install software from source how can we check whether we installed software or not.

you can't. if you want to install in a way that you can check, there are tools like checkinstall, but after the event it's impossible other than by guesswork and such.

what an immediate reply!! thanks for your timely response.thanks acid

In almost every case the executable that is produced by compiling from source is put in /usr/local/bin.
Browsing that folder should give you a pretty good idea of what has been compiled. It won't be complete because you can compile libraries of various kinds that don't go into /usr/local/bin but if you're really curious you can browse around the other /usr/local folders.
Cheers,
jdk

The advantage of packaging systems is that they maintain a database of installed tools. When compiling from source you have to keep track of information yourself.

The configure file usually allows to define a custom install path. Usually /usr/local or /opt are commonly used for this. Keeping all your own compilations in place gives some kind of a poor man's database with a single ls command.

Arch Linux

The only good "database" that would help you is to save the build tree for everything you install manually in a single location, for example $HOME/build or whatever. That way you always know what do you installed by hand, and more important, you can always make uninstall using that same tree, or a similar thing.

If you weren't careful enough to do that on first time then there's no way to know what did you install by hand in the past, as someone else said above.