UNIX and Linux Applications

Hello

I'm writing a program for managing accounts and groups in a linux system.
My problem is how to update the members of a group in the /etc/group file,if i have to add/remove those members.

total 3 variables for adding some new members to the group :

Code:

char **oldmembers=grp->gr_mem;        //members before 
char **newmembers;      //new members to be added
char **totalmembers;     //total members (new_old)

while *(oldmembers)
{
*totalmebers=*oldmembers;
totalmebers++
oldmembers++
}

I cant figure out how to continue using the totalmembers pointer from the point it stopped inside the while loop,to add the newmembers now
e.g

Code:

 while *(newmembers)
{
*totalmebers=*newmembers;
totalmebers++
newmembers++
}

so i the end i could have the total memebrs in order to use the setgrnam(struct group *grp) to parse the updated group struct


any help would be appreciated (and any different approach too)
Thanks

ok i'm done with adding,using the addgroup from the shell
any ideas for removing members?