Why is NSString returning null? - objective-c

Question

#import <Foundation/Foundation.h>
//-----Interface-----
#interface Person: NSObject{
int age;
int weight;
NSString *name;
}
-(void) print;
-(void) setAge: (int) a;
-(void) setWeight: (int) w;
-(void) setName: (NSString*) n;
#end
//-----Implementation-----
#implementation Person
-(void) print{
NSLog(#"%# is %i years old and my weight is %i pounds", name, age, weight);
}
-(void) setAge: (int) a{
age=a;
}
-(void) setWeight: (int) w{
weight=w;
}
-(void) setName: (NSString*) n{
name=n;
}
#end
//-----Main Program-----
int main(int argc, const char * argv[]) {
#autoreleasepool {
Person *james = [[Person alloc]init];
Person *bob = [[Person alloc]init];
[james setAge: 55];
[james setWeight: 400];
[james print];
[bob setAge: 80];
[bob setWeight: 150];
[bob print];
}
return 0;
}
It should return "james is 55 years old and my weight is 400 pounds" and "bob is 80 years old and my weight is 150 pounds"
But instead of "bob" and "james" I am getting "(null)"
Any ideas of why this could be happening?

Answer 1

You're not actually calling setName anywhere in your code ;) Try:
// ... other code happens here, then:
#autoreleasepool {
Person *james = [[Person alloc]init];
Person *bob = [[Person alloc]init];
[james setAge: 55];
[james setWeight: 400];
[james setName: #"james"]; // you need this
[james print];
[bob setAge: 80];
[bob setWeight: 150];
[bob setName: #"bob"]; // and this
[bob print];
}
In the end, bear in mind that just because you created a class instance with a particular name (in this case james and bob), doesn't explicitly set a property such as name.
You might try something a little clever like adding an initialization method to inside your class:
In your header/interface:
- (id) initWithName:(NSString*)name;
And in your implementation:
- (id) initWithName:(NSString*)name
{
self = [super init];
if (self != nil)
{
[self setName:name];
}
return self;
}
Then you can call:
Person *james = [[Person alloc]initWithName:#"james"];

Answer 2

it seems you never call something like [james setName:#"james"] so name property is never initialised