Zlib in Xcode using objective c
===

I am using below link :http://www.clintharris.net/2009/how-to-gzip-data-in-memory-using-objective-c/
as my CDTest.h and CDTest.m and in my TestAppDelegate.m i am calling these class with button action as

-(IBAction)Zipbtn:(id)sender{
    
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSLog(@"paths=%@",paths);
    NSString* dPath = [paths objectAtIndex:0];
    NSLog(@"dpaths=%@",dPath);
    
    NSString* txtfile = [dPath stringByAppendingPathComponent:@"test.txt"];
    NSLog(@"txtfile=%@",txtfile);

    NSData* data=[txtfile dataUsingEncoding:NSUTF8StringEncoding];
     NSLog(@"data=%@",data);
    
   CDTest *obj=[[CDTest alloc]init];
    [obj gzipData:data];
    
   
}
but showing warning instance method -gzipData not found also on running this code getting error :-[CDTest gzipData:]: unrecognized selector sent to instance 0x7f8d7a009070
Please help me out as i am new to Mac osx.