// Person.h

/*
* Objective C uses #import instead of #include
*/
#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>

/*
* Inheritance in Objective C is shown by a classname
* followed by a colon followed by another classname
* NSObject is the superclass for every Objective C class, either directly or indirectly
*/
@interface Person: NSObject
{
    //Instance data are declared here:
    @private
        NSString* name;
        int age;
}

//Methods are declared here:

/*
* Methods are defined like this
* -(<RETURN_TYPE>) <DESCRIPTION>: (<ARG_TYPE>) <ARG_NAME>
*/
-(Person*) initWithName: (NSString*) n andAge: (int) a;

-(NSString*) name;

-(int) age;

-(NSString*) speak;

@end

// Person.m

#import "Person.h"

@implementation Person

-(Person*) initWithName: (NSString*) n andAge: (int) a
{
    /*
     * Methods are called with [<CLASS> <METHOD>];
     * init is a method provided by NSObject that provides a default constructor
     */
    self = [super init];
    
    
    /*
     * if the super constructor returned a success, continue initialization
    */
    
    if (self)
    {
        /*
         * release and retain are memory management methods
         * retain increments the count of pointers to a location in memory
         * release does the opposite
         * Once the count is zero the memory is released
         */
        [n retain];
        [name release];
        name = n;
        
        /*
         * age is simply an int, and not a pointer
         * so it's pass-by-value
         */
        age = a;
    }
    
    /*
     * self is analagous to this in C++/Java
     */
    return self;
}

-(NSString*) name
{
    return name;
}

-(int) age
{
    return age;
}

-(NSString*) speak
{
    /*
     * stringWithFormat creates a new string using printf format
     * %@ inserts an NSObject
     * and you don' need to call the init method here, because the
     @ preceding the string constant initializes the string for you
     */
    NSString* result = [ [NSString alloc] initWithFormat:@"Hi.  My name is %@ and my age is %d.",
                        name, age];
    
    return result;
    
}

@end

// main.m

#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSString.h>
#import <stdio.h>
#import "Person.h"

int main(int argc, const char* argv[])
{
    /*
     * alloc reserves memory space for an object
     * NSAutoReleasePool is an automated Garbage collection mechanism
    */
    NSAutoreleasePool* pool = [ [NSAutoreleasePool alloc] init];
    NSString* name = [NSString stringWithString: @"GWatt"];
    Person* gwatt = [ [Person alloc] initWithName: name andAge: 500];
    
    /*
     * printf can't handle NSStrings so we use UTF8String to return a char array
    */
    printf("Name:\t%s\n", [ [gwatt name] UTF8String] );
    printf("Age:\t%d\n", [gwatt age] );
    printf("\n%s\n", [ [gwatt speak] UTF8String] );
    
    [gwatt release];
    
    return 0;
}