Multiple CheckBox

-(IBAction)ChkUnChk:(id)sender //To connect all buttons

{

    

    UIButton *btn=(UIButton *)sender;

    NSString *Str=[NSString stringWithFormat:@"%d",btn.tag];

    BOOL flag=   [selectedBtnarr containsObject:Str];

    

    if (flag==YES)

    {

        [btn setBackgroundImage:[UIImage imageNamed:@"A.jpg"]    forState:UIControlStateNormal];

        [selectedBtnarr removeObject:Str];

    }

    else

    {

        [selectedBtnarr addObject:Str];

        [btn setBackgroundImage:[UIImage imageNamed:@"che1.png"] forState:UIControlStateNormal];

    }

}