NSString *str=@"Hi,How r u"; 
NSArray *arr = [str componentsSeparatedByString:@","];
NSString *strSecond = [arr objectAtIndex:1];

NSMutableArray *arrSecond = [strSecond componentsSeparatedByString:@" "];
NSString *strHow = [arr objectAtIndex:0];
NSString *strAre = [arr objectAtIndex:1];
NSString *strYou = [arr objectAtIndex:2];

[arr removeObjectAtIndex:1];
[arr addObject:@","];
[arr addObject:strHow];
[arr addObject:strAre];
[arr addObject:strYou];  

arr 是所需数组。