while (1) {
    # display the menu
    print $menu, "\n\n";

    # get the user choice 
    print "Make your choice: ";
    chomp($choice = lc <STDIN>);

    # fulfill the user request 
    if ($choice eq 'a'){
        print "Enter a male name: ";
        chomp ($name1 = lc <STDIN>);
        }

    if (exists $son_father{$name1}) {
        print "Duplicate name -- try again!\n";
        } 
    else {
        print "Add a father: ";
        chomp ($add_dad = lc <STDIN>);
        $son_father{$name1} = {$add_dad}; 
        } 
        
    ...
    
    }  # end while loop