How to add numbers in a mutable array in iPhone?

You can only add NSObject subclasses in Cocoa containers. In your case, you will have to wrap your integers in NSNumber objects:

NSMutableArray *array = [NSMutableArray array];
for( int i = 0; i < 100; ++i )
{
   [array addObject:[NSNumber numberWithInt:i]];
}

To extract the values:

int firstValue = [[array objectAtIndex:0] intValue];

Use an NSNumber object:

[NSNumber numberWithInt:1];