How do I merge changes in Mercurial - mercurial

Question

I have used hg clone to get a working copy of a project on a local folder
hg clone http://example.com/prj
I want to modify some files to meet my needs. For example an original file looks like:
int main() {
cout << "hello";
return 0;
}
So I change that like this:
int main() {
int a = 0;
cout << "hello";
return 0;
}
Later the main repository changes and looks like this (compare to the first snippet):
int main() {
for (int i=0; i<10; i++ )
cout << "hello";
return 0;
}
Now when I run
hg pull
hg update
my change int a=0; is lost.

Answer 1

For a crash course of how distributed SCM's work, and moreover HOW to use them please read either
Joel Spolsky's excellent tutorial
Or:
This illustrated tutorial
Mecrurial in daily use
Actually, this does not happen, if you remember to hg commit after you make the change.
You will just have a repository with 2 heads, that you would need to hg merge e.g:
$ hg pull
pulling from /tmp/remote
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg merge
int main() { | int main() { | int main() {
int a = 0; | for (int i=0; i<10 ;| cout << "hello";
cout << "hello"; | cout << "hello";| ------------------------
return 0; | return 0; | return 0;
} | } | }
To learn how to use mercurial, please read the online book