#include <library.h>

void say(const int n);

  // that was a "prototype", a promise that a function exactly like that
  // will be defined before the end of the program. It lets us decide
  // what order things appear in, so we can put the important things
  // first and save the mere details until later

void main()
{ while (true)
  { print("number? ");
    const int x = read_int();
    say(x);
    new_line(); } }


const string small_names[] =
  { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", 
    "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", 
    "eighteen", "nineteen" };

const string ty_names[] = { "zero", "ten", "twenty", "thirty", "forty", "fifty",
    "sixty", "seventy", "eighty", "ninety" };


void say(const int n)
{ if (n < 0)
  { print("minus ");
    say(- n); }
    
  else if (n < 20)
    print(small_names[n]);
 
         // everything before this point guaranteed good.
         // if n < 20, say(n) WILL WORK CORRECTLY.
   
  else if (n < 100 && n%10 == 0)
    print(ty_names[n / 10]); 
    
  else if (n < 100)
  { say(n / 10 * 10);
    print("-");
    say(n % 10); }
 
         // everything before this point guaranteed good.
         // if n < 100, say(n) WILL WORK CORRECTLY.

  else if (n < 1000)
  { say(n / 100);
    print(" hundred");
    const int last_two = n % 100;
    if (last_two != 0)
    { print(" and ");
      say(last_two); } }
 
         // everything before this point guaranteed good.
         // if n < 1,000, say(n) WILL WORK CORRECTLY.

  else if (n < 1000000)
  { say(n / 1000);
    print(" thousand");
    const int last_three = n % 1000;
    if (last_three != 0)
    { if (last_three < 100)
        print(" and ");
      say(last_three); } }
 
         // everything before this point guaranteed good.
         // if n < 1,000,000, say(n) WILL WORK CORRECTLY.
   
  else
    print("I can't do it\n"); }