Newbie Objective C Error such as _main - objective-c

Question

I've been tinkering all day, and I can't seem to fix this error.
Here's the code:
//
// main.m
// Learning ObjC
//
// Created by Nickirv on 8/9/15.
// Copyright (c) 2015 Nickirv. All rights reserved.
//
#import <Foundation/Foundation.h>
#interface Person: NSObject{
int age;
int weight;
}
-(void) print;
-(void) setAge: (int) a;
-(void) SetWeight: (int) w;
#end
And it outputs this issue:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I would appreciate any help! Thank you very much!

Answer 1

You can't delete the main boilerplate code:
int main(int argc, const char * argv[]) {
#autoreleasepool {
}
return 0;
}
In the end Objective-C is "C" and the program starts execution by calling main. Additionally Objective-C code needs to execute in an autoreleasepool.
You define class #interfaces and #implemtations outside of (generally above) the boilerplate but the first line of code to run must be within the autoreleasepool scope {}.
Here is an example Objective-C program similar to what the OP seems to want using #properties for simplicity and demonstration.
It is important to study Objective-C documentation until the following code is fully understood, td;dr does not work for this.
#import <Foundation/Foundation.h>
#interface Person: NSObject
#property int age;
#property int weight;
- (void)print;
#end
#implementation Person : NSObject
- (void)print {
printf("Age: %i, weight: %i", self.age, self.weight);
}
#end
int main(int argc, const char * argv[]) {
#autoreleasepool {
Person *don = [[Person alloc] init];
don.weight = 130;
don.age = 23;
[don print];
}
return 0;
}
Output:
Age: 23, weight: 130