After change, how can I see the output of changed code? Do I have to build each time?
Yes, that's how compiled languages work. Note, however, that the build system will skip a lot of work it doesn't have to do; only generated C code that changes between compilations needs to be recompiled. Also, you can parallelize the build by running
make -j instead of
Practically speaking, compile times for a small program like that are very quick. It depends on your CPU, but we're talking maybe a couple of seconds for an incremental build.
Let's say after 50 changes I am satisfies now with modified code? How can I install that app so it always give me updated ( with 50 changes ) version of app?
If you've passed the right options to CMake, you can just
sudo make install to install system-wide. However, most experienced developers I know prefer to stick to the packaged versions for their system wide install when possible. jhbuild makes for a great development environment if you have multiple bleeding-edge components which need to work together.