// This program demonstrates several new concepts, including:
//   - String methods (charAt, length, etc.)
//   - fencepost loops
//   - String cumulative "sum"
//   - while loops
//   - sentinel loops
import java.util.*;

public class LoopPractice {
   public static void main(String[] args) {
      System.out.println(doubleLetters("abcde"));
      System.out.println(doubleLetters("Mississippi"));
      System.out.println(doubleLetters("abracadabra"));
      System.out.println();
      
      spellOut("hello");
      spellOut("CSE142");
      spellOut("Happy Birthday");
      System.out.println();
      
      printPowers(2, 100);
      printPowers(10, 100000);

      printPowers2(2, 100);
      printPowers2(10, 100000);
      System.out.println();
      
      Scanner console = new Scanner(System.in);
      System.out.println(sumAll(console));
   }
   
   // Returns a new String with each character from the given String
   //   doubled.
   // e.g. hello -> hheelllloo
   // Note that this is a form of a cumulative sum using Strings!
   //
   // String word - the String whose letters should be doubled
   public static String doubleLetters(String word) {
      String result = "";
      for (int i = 0; i < word.length(); i++) {
         // String letter = word.substring(i, i + 1);
         char letter = word.charAt(i);
         result = result + letter + letter;
      }
      return result;
   }   
   
   // Prints out the the characters in the given String separated
   //  by dashes.
   // e.g. hello -> h-e-l-l-o
   //
   // String word - the String to print
   public static void spellOut(String word) {
      System.out.print(word.charAt(0));
      for (int i = 1; i < word.length(); i++) {
         System.out.print("-" + word.charAt(i));
      }
      System.out.println();
   }
   
   // Alternate version of spellOut that removes the last instance
   //   of the fencepost instead of the first.
   //
   // String word - the String to print
   public static void spellOutAlt(String word) {
      for (int i = 0; i < word.length() - 1; i++) {
         System.out.print(word.charAt(i) + "-");
      }
      System.out.println(word.charAt(word.length() - 1));
   }
   
   // Print out the powers of base up to the first power of base that is 
   //   greater than last
   // e.g. 2, 10 -> 2, 4, 8, 16, 32, 64, 128
   //
   // int base - the base of the powers to be printed
   // int last - the number after which to stop printing powers
   public static void printPowers(int base, int last) {
      // indefinite loop
      int power = base;
      System.out.print(power);    
      while (power < last) {
         System.out.print(", ");    
         power *= base;             
         System.out.print(power); 
      }
      System.out.println();
   }

   // Read in integers from the user until a -1 is typed,
   //   then return the sum of all numbers typed (not including
   //   the -1).
   // 
   // Scanner console - the Scanner to use for input
   public static int sumAll(Scanner console) {
      int total = 0;
      System.out.print("Enter an integer (-1 to stop): ");
      int number = console.nextInt();
      while (number != -1) {
         total += number;
         System.out.print("Enter an integer (-1 to stop): ");
         number = console.nextInt();
      }
      
      return total;
   }   
}