EXC_BAD_ACCESS iOS error - iphone

Question

I know, I know. I've Google and searched here but can't figure out what's going on.
Anyway, i'm getting this error when using the following code, i'm sure it's something small. I know it's to do with memory management and down to how i'm handling my object in the main method.
Here's my main code:
Person *p1 = [[Person alloc] init];
[p1 initWithFirstname:#"John" lastname:#"Doe" andAge:23];
outputText.text = [p1 getDetails]; // App crashes inside getDetails
Then in the person class here's the two relevant methods:
-(Person *)initWithFirstname:(NSString *)_firstname lastname:(NSString *)_lastname andAge:
(int)_age {
self = [super init];
if(self) {
self.firstname = _firstname;
self.lastname = _lastname;
self.age = _age;
}
return self;
}
-(NSString *)getDetails {
return [NSString stringWithFormat:#"%# %#, %#", firstname, lastname, age];
}

Answer 1

Judging by your init method, age is an int which means the format specifier is wrong. Try this:
-(NSString *)getDetails
{
return [NSString stringWithFormat:#"%# %#, %d", firstname, lastname, age];
// ^^ format specifier for an int
}

Answer 2

You've written an initialization method, then called init twice. Just try:
Person *p1 = [[Person alloc] initWithFirstname:#"John" lastname:#"Doe" andAge:23];
outputText.text = [p1 getDetails];

Answer 3

You're first calling the default init of your newly allocated object. That init returns a pointer to your object which you store in p1. Then you call initWithFirstname:lastname:andAge: on p1, which is wrong as you've already called another initializer first. You're only supposed to run one initializer.
You need to do:
Person *p1 = [[Person alloc] initWithFirstname:#"John" lastname:#"Doe" andAge:23];
But your crash stems from the fact that you pass the number 23 to the format specifier %#. You need to use %d for the age instead. Also, you should retain the first and last name (and release them in your dealloc) to avoid any crashes later on when using non-const strings.
What happens is that because of %#, the NSLog tries to treat the 23 as a pointer to an object and wants to call the description method of the supposed object. But 23 is an invalid/unused address, and trying to access the memory at that "address" is what makes your app crash.