'AClass' may not response to 'FunctionA' (Objective-C) - objective-c

Question

Something about inheritance, I have two class here: female, the subclass of human, and human, it can run but showing issues.
Two issues here:
main.m:29:10: 'human' may not respond to 'setSexy:'
main.m:30:10: 'human' may not respond to 'isSexy'
main.m
#import <Foundation/Foundation.h>
#import "female.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
human *sexyGirl = [[female alloc] init];
[sexyGirl setName:#"SexyGirl"];
[sexyGirl setGender:0];
[sexyGirl setSexy:1];
[sexyGirl isSexy];
}
return 0;
}
female.h
#import "human.h"
#interface female : human {
BOOL sexy;
}
#property BOOL sexy;
-(void)isSexy;
#end
human.h
#import <Foundation/Foundation.h>
#interface human : NSObject {
NSInteger *hp;
NSString *name;
BOOL gender;
}
#property (assign, nonatomic) NSInteger *hp;
#property (assign, nonatomic) NSString *name;
#property (assign, nonatomic) BOOL gender;
-(void) walk;
#end

Answer 1

There is no method name isSexy and setSexy in human class
You should change this human *sexyGirl = [[female alloc] init];
to this female *sexyGirl = [[female alloc] init];

Answer 2

when you do : human *sexyGirl = [[female alloc] init];
you upcast the female to human. all the extra information (extra methods) a female has are still there but no longer visible
you can only work with what a human has from then on OR you downcast the variable again.
[(female*)sexyGirl setSexy:1];
[(female*)sexyGirl isSexy]
alternativly never downcast it and declare it as female * all the way