Why these objects always have same value?

[new2objectivec]

Hi,

This is my first post, just started learning objective-C. Got a problem while testing some basic objects. I have a "Tire" object, when initialised I assigned it a random number. But when I created 4 of them, how come they all have the same number?
Any help appreciated. Thanks!

//Tire.h
#import <Foundation/Foundation.h>

@interface Tire : NSObject {
	NSString *serialNo;
}

@property (nonatomic) NSString *serialNo;
@end

//Tire.m
#import "Tire.h"


@implementation Tire
@synthesize serialNo;

-(id) init {
	if (self=[super init]) {
		srandom(time(0));	
		int n = (random() % (100)) + 1;
		serialNo = [[NSString alloc] initWithFormat:@"ABC%d",n];
	}
	return (self);
}

-(NSString *) description {
	return (@"I am a tire, serialNo is %@",self.serialNo);
}

-(void) dealloc {
	[serialNo release];
	[super dealloc];
}

//CmdObjTest.m
#import <Foundation/Foundation.h>
#import "Tire.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // insert code here...
    NSLog(@"Hello, World!");
	
	Tire *n1 = [[Tire alloc] init];
	
	NSLog(@"Tire1: %@",n1);
	
	Tire *n2 = [[Tire alloc] init];
	
	NSLog(@"Tire2: %@",n2);
	
	Tire *n3 = [[Tire alloc] init];
	
	NSLog(@"Tire3: %@",n3);
	
    [pool drain];
    return 0;
}

@end

This is the output, I was expecting each object showing different number??

2011-06-01 20:42:50.885 CmdObjTest[1621:a0f] Hello, World!
2011-06-01 20:42:50.888 CmdObjTest[1621:a0f] Tire1: ABC25
2011-06-01 20:42:50.888 CmdObjTest[1621:a0f] Tire2: ABC25
2011-06-01 20:42:50.888 CmdObjTest[1621:a0f] Tire3: ABC25

2011-06-01 20:46:49.333 CmdObjTest[1647:a0f] Hello, World!
2011-06-01 20:46:49.335 CmdObjTest[1647:a0f] Tire1: ABC96
2011-06-01 20:46:49.336 CmdObjTest[1647:a0f] Tire2: ABC96
2011-06-01 20:46:49.336 CmdObjTest[1647:a0f] Tire3: ABC96

[iisword]

Try arc4random() instead of random()

[dapis]

You should seed the random number generator with a single call to

srandom(time(NULL));

in the applicationDidFinishLaunching method (of the app delegate) and not in the init method of your class.

Or, vastly better, do as iisword said and use arc4random. It is a far better random number generator and does not need to be seeded.

[new2objectivec]

As suggested, I changed the init method to as below

-(id) init {
if (self=[super init]) {
	//srandom(time(0));
	
	int n = (arc4random() % (100)) + 1;
	
	serialNo = [[NSString alloc] initWithFormat:@"ABC%d",n];
	
}
return (self);
}

And it works beautifully! Thanks a lot!

The result:

2011-06-03 19:19:40.849 CmdObjTest[237:a0f] Hello, World!
2011-06-03 19:19:40.852 CmdObjTest[237:a0f] Tire1: ABC46
2011-06-03 19:19:40.852 CmdObjTest[237:a0f] Tire2: ABC13
2011-06-03 19:19:40.853 CmdObjTest[237:a0f] Tire3: ABC68

2011-06-03 19:21:19.068 CmdObjTest[264:a0f] Hello, World!
2011-06-03 19:21:19.070 CmdObjTest[264:a0f] Tire1: ABC45
2011-06-03 19:21:19.070 CmdObjTest[264:a0f] Tire2: ABC62
2011-06-03 19:21:19.071 CmdObjTest[264:a0f] Tire3: ABC12