I have repeated error 3rd time, but I could not found that what is mean of use of undeclared identifier ..

I wrote that program on function in objective-C

#import <Foundation/Foundation.h>
 
@interface Add:NSObject 
 
/* method declaration */
 - (int)add:(int)a andNum2:(int)b;

@end

@implementation Add 
 
/* method returning the max between two numbers */
 - (int)add:(int)a andNum2:(int)b {

/* local variable declaration */
int sum = a +b;
return sum;
}
@end
  NSLog(@"sum is : %d", sum);// error this line     
  return 0;
}