#include "library.h"

   // PROTOTYPES, allow functions to be used before their definitions
void print_0_to_19(const int d);
     // absolutely tested and perfect, speaks any number 0 .. 19

void print_multiple_of_10(const int d);
     // perfect, says any number 10, 20, 30, ..., up to 90

void print_20_to_99(const int n);
     // perfect for any number 20, 21, 22, ..., 99

void print_100_to_999(const int n);
     // perfect for any number 100 ... 999

/* The various versions of say_number that we went through
   are all in this file. All but the final one has been
   turned into a comment */


/*
  void say_number(const int n)
       // this function is guaranteed to work perfectly
       // for any int 0 ... 999.
       // say_number(x) is guaranteed to write the number x perfectly
       // in english regardless of how or where it is used, so long as
       // 0<=x and x<1000.
  { if (n < 20)
      print_0_to_19(n);
      
    else if (n < 100)
      print_20_to_99(n);
    
    else if (n < 1000)
      print_100_to_999(n); }
*/

/*
  // because we are guaranteed that say_number works for 0 ... 999,
  // we know that this code will work for 1000 ... 999999

      say_number(n / 1000);
      print(" thousand");
      const int last3 = n % 1000;
      if (last3 > 0)
      { print(" ");
        if (last3 < 100)
          print("and ");
        say_number(last3); }

  // therefore this:

  void say_number(const int n)
       // this function is guaranteed to work perfectly
       // for any int 0 ... 999999.
       // say_number(x) is guaranteed to write the number x perfectly
       // in english regardless of how or where it is used, so long as
       // 0<=x and x<1000000.
  { if (n < 20)
      print_0_to_19(n);
      
    else if (n < 100)
      print_20_to_99(n);
    
    else if (n < 1000)
      print_100_to_999(n);

    else if (n < 1000000)
    { say_number(n / 1000);
      print(" thousand");
      const int last3 = n % 1000;
      if (last3 > 0)
      { print(" ");
        if (last3 < 100)
          print("and ");
        say_number(last3); } } }
*/

/*
  // and by the same reasoning ...

  void say_number(const int n)
       // this function is guaranteed to work perfectly
       // for any int 0 ... 999999999.
       // say_number(x) is guaranteed to write the number x perfectly
       // in english regardless of how or where it is used, so long as
       // 0<=x and x<1000000000.
  { if (n < 20)
      print_0_to_19(n);
      
    else if (n < 100)
      print_20_to_99(n);
    
    else if (n < 1000)
      print_100_to_999(n);

    else if (n < 1000000)
    { say_number(n / 1000);
      print(" thousand");
      const int last3 = n % 1000;
      if (last3 > 0)
      { print(" ");
        if (last3 < 100)
          print("and ");
        say_number(last3); } }

    else if (n < 1000000000)
    { say_number(n / 1000000);
      print(" million");
      const int last6 = n % 1000000;
      if (last6 > 0)
      { print(" ");
        if (last6 < 100)
          print("and ");
        say_number(last6); } } }
*/

/*
  // and of course

  void say_number(const int n)
       // this function is guaranteed to work perfectly
       // for any positive int.
       // ints only go up to about 2000000000.
  { if (n < 20)
      print_0_to_19(n);
      
    else if (n < 100)
      print_20_to_99(n);
    
    else if (n < 1000)
      print_100_to_999(n);

    else if (n < 1000000)
    { say_number(n / 1000);
      print(" thousand");
      const int last3 = n % 1000;
      if (last3 > 0)
      { print(" ");
        if (last3 < 100)
          print("and ");
        say_number(last3); } }

    else if (n < 1000000000)
    { say_number(n / 1000000);
      print(" million");
      const int last6 = n % 1000000;
      if (last6 > 0)
      { print(" ");
        if (last6 < 100)
          print("and ");
        say_number(last6); } }

    else
    { say_number(n / 1000000000);
      print(" billion");
      const int last9 = n % 1000000000;
      if (last9 > 0)
      { print(" ");
        if (last9 < 100)
          print("and ");
        say_number(last9); } } }
*/

  // and finally

void say_number(const int n)
     // this function is guaranteed to work perfectly
     // for any int.
  { if (n < 0)
    { print("negative ");
      say_number(- n); }

    else if (n < 20)
      print_0_to_19(n);
      
    else if (n < 100)
      print_20_to_99(n);
    
    else if (n < 1000)
      print_100_to_999(n);

    else if (n < 1000000)
    { say_number(n / 1000);
      print(" thousand");
      const int last3 = n % 1000;
      if (last3 > 0)
      { print(" ");
        if (last3 < 100)
          print("and ");
        say_number(last3); } }

    else if (n < 1000000000)
    { say_number(n / 1000000);
      print(" million");
      const int last6 = n % 1000000;
      if (last6 > 0)
      { print(" ");
        if (last6 < 100)
          print("and ");
        say_number(last6); } }

    else
    { say_number(n / 1000000000);
      print(" billion");
      const int last9 = n % 1000000000;
      if (last9 > 0)
      { print(" ");
        if (last9 < 100)
          print("and ");
        say_number(last9); } } }



void print_100_to_999(const int n)
{ const int hundreds = n / 100,
            remainder = n % 100;
  say_number(hundreds);
  print(" hundred");
  if (remainder != 0)
  { print(" and ");
    say_number(remainder); } }	    

void print_20_to_99(const int n)
                         // example:   if     n    is 47
                         //          then  n/10*10 is 40
                         //           and   n%10   is  7
{ print_multiple_of_10(n/10*10);
  if (n % 10 != 0)
  { print(" ");
    print_0_to_19(n%10); } }

void test(const int n)
{ print("testing ");
  print(n);
  print(": '");
  say_number(n);
  print("'\n");; }


void main()
{ test(27);
  test(138);
  test(509);
  test(999);
  test(12);
  test(4);
  test(40);
  while (true)
  { print("enter a test number (negative to stop): ");
    const int t = read_int();
    if (t < 0) break;
    test(t); }
  print("Test over\n"); }

void print_0_to_19(const int d)
{ if (d == 0)
    print("zero");
  else if (d == 1)
    print("one");
  else if (d == 2)
    print("two");
  else if (d == 3)
    print("three");
  else if (d == 4)
    print("four");
  else if (d == 5)
    print("five");
  else if (d == 6)
    print("six");
  else if (d == 7)
    print("seven");
  else if (d == 8)
    print("eight");
  else if (d == 9)
    print("nine");
  else if (d == 10)
    print("ten");
  else if (d == 11)
    print("eleven");
  else if (d == 12)
    print("twelve");
  else if (d == 13)
    print("thirteen");
  else if (d == 14)
    print("fourteen");
  else if (d == 15)
    print("fifteen");
  else if (d == 16)
    print("sixteen");
  else if (d == 17)
    print("seventeen");
  else if (d == 18)
    print("eighteen");
  else if (d == 19)
    print("nineteen");
  else 
    print("\n**** ERROR ****\n"); }

void print_multiple_of_10(const int d)
{ if (d == 10)
    print("ten");
  else if (d == 20)
    print("twenty");
  else if (d == 30)
    print("thirty");
  else if (d == 40)
    print("forty");
  else if (d == 50)
    print("fifty");
  else if (d == 60)
    print("sixty");
  else if (d == 70)
    print("seventy");
  else if (d == 80)
    print("eighty");
  else if (d == 90)
    print("ninety");
  else 
    print("\n**** ERROR ****\n"); }