User permitted to run command,execute program as root and after execution, exit root
 

when a command is typed(i.e. /path/to/the/program), as a normal user, he should be able to run that command , execute that program as ROOT and log out root after the execution is completed.
Only one user should be able to do it.
Hence, I have created a new user vj and added the following command in visudo:
Now user vj will be able to typein the command.

What I need is that the program which is been called must run as if it is run by a root user,and when the program is completely executed, exit the root user.

How do I proceed?

that is the command sudo:
sudo /path/to/the/program
That's why you used visudo to modify configuration.

The above command will allow the user to call the program, but if there are n other things that are being executed inside the original program.
The user vj has no rights to execute them. So, do I explicitly have to allow the user to execute the n number of commands?

No, if that program starts other programs those other programs inherit the privilege of the program that started them. No further configuration is needed. For security, make sure that those other programs that are started are trusted and that the user can't use them to alter the configuration of the sudo program.

I have called "ifup eth0" in the program, and it gives me an error

you have to call the program using sudo:

So, it means that if I add the user to visudo and then run it, it should not give me an error.
Adding it to visudo is as good as writing sudo before the command right?

vi is an editor, visudo means edit the configuration file of sudo (see: man visudo).

"Adding to visudo" is exaclty the same as "writing sudo rights".

No, visude and sudo have to be used in conjunction. You use visude to tell the sudo program which user can run specific programs as root. To actually do that you have to put sudo in front of those programs.

But when I add this command to the visudo it gives me an error :(

@TobiSGD I think I got it. U mean that I should add ifup and ifdown in viduso and should write sudo /sbin/ifup in the program where I am calling it right?

Exactly.

It's working.. thankyou :)