can't make addition in NSMutableArray obectatindex - iphone

Question

for(int i=0; i<[arrMaintenanceDetail count]; i++){
for(int j=0; j<[[arrMaintenanceCategory valueForKey:#"maintenanceCategory"] count]; j++){
if([[arrMaintenanceDetail objectAtIndex:i] isEqualToString:[[[arrMaintenanceCategory valueForKey:#"maintenanceCategory"]objectAtIndex:i] stringValue]]){
[arrTotalValues objectAtIndex:i] += [arrTotalValues insertObject:[[[arrMaintenanceCategory valueForKey:#"cost"] objectAtIndex:j] integerValue] atIndex:i];
}
}
}
I want to add (make addition of integer values) value from
[[[arrMaintenanceCategory valueForKey:#"cost"] objectAtIndex:j] integerValue];
Whenever loop changes its value.
I want new value from objectAtIndex:j to be added to its previous value and store it for future use.
I will have 4 objects in arrTotalValues (NSMutableArray).
So what should I do ??

Answer 1

You cannot keep integers in NSMutableArray. Use NSNumber to keep integer values in your NSMutableArray as objects.
You didn't provide enough information to give you 100% working code, but try something like that:
NSMutableArray* arrTotalValues = [NSMutableArray array];
for(int i=0; i<[arrMaintenanceDetail count]; i++)
{
NSNumber* totalValue = [NSNumber numberWithInt:0];
for(int j=0; j<[[arrMaintenanceCategory valueForKey:#"maintenanceCategory"] count]; j++)
{
if([[[arrMaintenanceDetail objectAtIndex:i] stringValue] isEqualToString:[[[arrMaintenanceCategory valueForKey:#"maintenanceCategory"] objectAtIndex:i] stringValue]])
{
int newTotalValue = [totalValue intValue] + [[[arrMaintenanceCategory valueForKey:#"cost"] objectAtIndex:j] integerValue];
totalValue = [NSNumber numberWithInt:newTotalValue];
}
}
[arrTotalValues addObject:totalValue];
}