Hexlet:: OS X #2, 10 http://hexlet.org/lesson/osx_2_10/

City.h

//
//  City.h
//  Hexlet Metropolis
//
//  Created by Roman Timashev on 10/11/13.
//  Copyright (c) 2013 Roman Timashev's Company. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface City : NSObject{
    NSString* name;
    int age;
    int population;
}

-(void) setName:(NSString*) cityName age:(int) cityAge population:(int) cityPopulation;
-(NSString*) getName;
-(int) getAge;
-(int) getPopulation;

-(void) nextDay;

@end

City.m

//
//  City.m
//  Hexlet Metropolis
//
//  Created by Roman Timashev on 10/11/13.
//  Copyright (c) 2013 Roman Timashev's Company. All rights reserved.
//

#import "City.h"

@implementation City{

}

-(void) setName:(NSString *)cityName age:(int)cityAge population:(int)cityPopulation{
    name = cityName;
    age = cityAge;
    population = cityPopulation;
}

-(NSString*) getName{
    return name;
}

-(int) getAge{
    return age;
}

-(int) getPopulation{
    return population;
}

-(void) nextDay{
    population += arc4random_uniform(population * 0.1);
    population -= arc4random_uniform(population * 0.1);
}

@end

main.m

//
//  main.m
//  Hexlet Metropolis
//
//  Created by Roman Timashev on 10/11/13.
//  Copyright (c) 2013 Roman Timashev's Company. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "City.h"
#import "Metropolis.h"

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        City *city = [[City alloc] init];
        [city setName:@"Vice City" age:300 population:500000];
        
        for(int i=0; i<10; i++){
            [city nextDay];
            NSLog(@"%@ population %i", [city getName], [city getPopulation]);
        }
        
        Metropolis *polis = [[Metropolis alloc] init];
        [polis createCity:@"Saint Petersburg" withPopulation:5500000 atIndex:0];
        [polis createCity:@"Pushkin" withPopulation:100000 atIndex:1];
        [polis createCity:@"Cronshtadt" withPopulation:50000 atIndex:2];
        [polis createCity:@"Gatchina" withPopulation:60000 atIndex:3];
        [polis createCity:@"Pavlovsk" withPopulation:30000 atIndex:4];
        [polis createCity:@"Petergoph" withPopulation:15000 atIndex:5];
        [polis createCity:@"Shlisselburg" withPopulation:15000 atIndex:6];
        [polis createCity:@"Vigorg" withPopulation:100000 atIndex:7];
        [polis createCity:@"Kuzmolovo" withPopulation:3000 atIndex:8];
        [polis createCity:@"Vsevolozhsk" withPopulation:25000 atIndex:9];
        
        for(int i=0; i<[polis numberOfCities]; i++){
            [[polis cityAtIndex:i] nextDay];
            City *city = [polis cityAtIndex:i];
            NSLog(@"%@ population %i", [city getName], [city getPopulation]);
        }
    }
    return 0;
}

Metropolis.h

//
//  Metropolis.h
//  Hexlet Metropolis
//
//  Created by Roman Timashev on 10/11/13.
//  Copyright (c) 2013 Roman Timashev's Company. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "City.h"

@interface Metropolis : NSObject
-(void) createCity: (NSString*) name withPopulation: (int) population atIndex: (int) index;
-(City*) cityAtIndex:(int) index;
-(int) numberOfCities;
@end

Metropolis.m

//
//  Metropolis.m
//  Hexlet Metropolis
//
//  Created by Roman Timashev on 10/11/13.
//  Copyright (c) 2013 Roman Timashev's Company. All rights reserved.
//

#import "Metropolis.h"

@implementation Metropolis{
    NSMutableArray *cities;
}
-(id) init{
    self = [super init];
    cities = [[NSMutableArray alloc] initWithCapacity:10];
    return self;
}

-(void) createCity:(NSString *)name withPopulation:(int)population atIndex:(int)index{
    City *city = [[City alloc] init];
    [city setName:name age:0 population:population];
    
    [cities insertObject:city atIndex:index];
}

-(City*) cityAtIndex:(int)index{
    return cities[index];
}

-(int) numberOfCities{
    return (int)[cities count];
}
@end