文字列が等しいかどうか判断する簡単なプログラム ref: http://qiita.com/items/bd55613d94283a9f7dc0

AppDelegate.h

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate> {
    IBOutlet NSTextField* field1;
    IBOutlet NSTextField* field2;
    IBOutlet NSTextField* result;
}

@property (assign) IBOutlet NSWindow *window;

- (IBAction)isEqual:(id)sender;

@end

AppDelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
}

- (IBAction)isEqual:(id)sender {
    if ([[field1 stringValue] isEqualTo:[field2 stringValue]]) {
        [result setStringValue:@"等しい"];
    } else {
        [result setStringValue:@"等しくない"];
    }
}

@end

main.c

#import <Cocoa/Cocoa.h>

int main(int argc, char *argv[])
{
    return NSApplicationMain(argc, (const char **)argv);
}