java.util.UnknownFormatConversionException: Conversion = '.' (Look around Formatter.java line 2579)

public class Programmers {

  public void printMenu() {
    String[] programmers = {
            "Yukihiro Matsumoto",
            "David Nolen",
            "Grace Hopper",
            "Linus Torvalds",
            "You"
    };

    System.out.println("Choose a programmer:");
    for (int i = 0; i < programmers.length; i++) {
      System.out.printf("d%. %s%n", i+1, programmers[i]);
    }
    // TODO: Print out a menu by looping through the programmers array.
    /*
      The menu should be in the form of (each on a line of its own, starting with 1):
      1. Yukihiro Matsumoto
      2. David Nolen
      ...
    */


  }

}