Ok so I populate the array like this:
NSMutableArray *participants;
for(int i = 0; i < sizeofpm; i++){
NSDictionary *pmpart_dict = [pm_participant
So, I as some of the other answer have stated, you're missing your initializer for participants. However, judging by your use of setValue:forKey:, and how you appear to be structuring your data, you're not looking for NSMutableArray, but instead NSMutableDictionary. Arrays are simply lists, whereas dictionaries maintain key-value relationships, which you appear to be attempting to leverage.
Try this:
// some classes provide shorthand for `alloc/init`, such as `dictionary`
NSMutableDictionary *participants = [NSMutableDictionary dictionary];
for(int i = 0; i < sizeofpm; i++){
NSDictionary *pmpart_dict = [pm_participants objectAtIndex:i];
NSString *pmpart_email = [pmpart_dict objectForKey:@"email"];
NSString *pmpart_email_extra = [@"pm" stringByAppendingString:pmpart_email];
[participants setValue:pmpart_email forKey:pmpart_email_extra];
NSLog(@"%@", participants);
}
This will give you a dictionary in the form of
{
pmpart_email_extra: pmpart_email
}