NSMutableArray *selected;
decleare it in you viewcontroller.h file..
selected =[[NSMutableArray alloc]init];
for (int i=0; i<[YOUR_ARRAY count]; i++) // Number of Rows count
        {
            [selected addObject:@"NO"];
        }
add same number of "NO" in selected array using above code for that you had to replace YOUR_ARRAY with your data array that you show in table.
    if(![[selected objectAtIndex:indexPath.row] isEqualToString:@"NO"])
{
    cell.accessoryType=UITableViewCellAccessoryCheckmark;
}
else
{
    cell.accessoryType=UITableViewCellAccessoryNone;
}
put above code in your -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)path {
UITableViewCell *cell = [tableView cellForRowAtIndexPath:path];
if (cell.accessoryType == UITableViewCellAccessoryNone) {
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
    [selected replaceObjectAtIndex:path.row withObject:@"YES"];
} else {
    cell.accessoryType = UITableViewCellAccessoryNone;
    [selected replaceObjectAtIndex:path.row withObject:@"NO"];
}
}
also put this to work correctly..