Extract a NSDictionary from a NSMutableArray - objective-c

Question

I need to extract a NSDictionary from a NSMutableArray, and extract an object from that dictionary.
The code should be quite easy, but I keep having a SIGABRT error on the NSDictionary declaration.
-(void)calcolaConto {
conto = [[NSNumber alloc] initWithDouble:0];
for (int i=0; [shoppingListItems count]; ++i) {
NSDictionary *dictVar = (NSDictionary *) [shoppingListItems objectAtIndex:i]; //<-- SIGABRT
NSNumber *IO = (NSNumber *) [dictVar objectForKey:#"incout"];
NSNumber *priceValue = (NSNumber *) [dictVar objectForKey:#"price"];
if ([IO isEqualToNumber:[NSNumber numberWithInt:0]]) {
conto = [NSNumber numberWithDouble:([conto doubleValue] + [priceValue doubleValue])];
} else if ([IO isEqualToNumber:[NSNumber numberWithInt:1]]) {
conto = [NSNumber numberWithDouble:([conto doubleValue] - [priceValue doubleValue])];
}
NSLog(#"Valore %#", conto);
}
}
"shoppingListItems" is created in this way:
NSMutableDictionary *rowDict = [[NSMutableDictionary alloc] initWithCapacity:6];
[rowDict setObject:primaryKeyValue forKey: ID];
[rowDict setObject:itemValue forKey: ITEM];
[rowDict setObject:priceValue forKey: PRICE];
[rowDict setObject:groupValue forKey: GROUP_ID];
[rowDict setObject:incOut forKey:INC_OUT];
[rowDict setObject:dateValue forKey: DATE_ADDED];
[shoppingListItems addObject: rowDict];

Answer 1

The problem is that your loop never stops. You should use:
for (NSUInteger i = 0; i < [shoppingListItems count]; i++) {
or:
for (NSDictionary* dictVar in shoppingListItems) {
so that you do not try to access an element that is out of bounds. In your
current loop i will be incremented until it reaches [shoppingListItems count]
which is beyond the end of the array, so objectAtIndex will throw an exception.