99 Bottles of Beer

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Language C++

(extreme template metaprogramming)

Date:	04/20/05
Author:	Richard Wolf
URL:	n/a
Comments:	5
Info:	n/a
Score:	(3.54 in 54 votes)

/* Richard Wolf, 2002

99 bottles of beer on the wall in an extreme template-metaprogramming style.  
It uses template specialisation to decided how to print numbers, whether 
'bottles' should be plural, and to finish the song correctly.  
Macros are used to generate the large number of specialisations required for
printing numbers nicely, eg 45 printed as "forty five" with pretty_print<45>().

Note that this will probably no compile immediately, since it requires the 
compiler to instantiate templates to a depth of (number of bottles + 4).  
Either reduce the number of starting bottles, or increase the maximum 
template depth on your compiler. 

Eg. using g++ use the -ftemplate-depth-103 command line option.

Tested on gcc, other compilers at your risk
*/

#include <iostream>

using namespace std;

template<bool small, int I>
struct pretty_printer;

#define SMALL_PRETTY_PRINTER(num, string) \
template<>\
struct pretty_printer<true, num>\
{\
    static void print()\
    {\
        cout << string;\
    }\
};

SMALL_PRETTY_PRINTER(0, "No")
SMALL_PRETTY_PRINTER(1, "One")
SMALL_PRETTY_PRINTER(2, "Two")
SMALL_PRETTY_PRINTER(3, "Three")
SMALL_PRETTY_PRINTER(4, "Four")
SMALL_PRETTY_PRINTER(5, "Five")
SMALL_PRETTY_PRINTER(6, "Six")
SMALL_PRETTY_PRINTER(7, "Seven")
SMALL_PRETTY_PRINTER(8, "Eight")
SMALL_PRETTY_PRINTER(9, "Nine")
SMALL_PRETTY_PRINTER(10, "Ten")
SMALL_PRETTY_PRINTER(11, "Eleven")
SMALL_PRETTY_PRINTER(12, "Twelve")
SMALL_PRETTY_PRINTER(13, "Thirteen")
SMALL_PRETTY_PRINTER(14, "Fourteen")
SMALL_PRETTY_PRINTER(15, "Fifteen")
SMALL_PRETTY_PRINTER(16, "Sixteen")
SMALL_PRETTY_PRINTER(17, "Seventeen")
SMALL_PRETTY_PRINTER(18, "Eighteen")
SMALL_PRETTY_PRINTER(19, "Nineteen")

#undef SMALL_PRETTY_PRINTER

template<int ones>
inline void 
print_ones();

#define ONES_PRINTER(ones, string) \
template<> \
inline void \
print_ones<ones>() \
{\
  cout << string;\
}

ONES_PRINTER(0, " ")
ONES_PRINTER(1, " one")
ONES_PRINTER(2, " two")
ONES_PRINTER(3, " three")
ONES_PRINTER(4, " four")
ONES_PRINTER(5, " five")
ONES_PRINTER(6, " six")
ONES_PRINTER(7, " seven")
ONES_PRINTER(8, " eight")
ONES_PRINTER(9, " nine")

#undef ONES_PRINTER

template<int tens>
inline void
print_tens();

#define TENS_PRINTER(tens, string) \
template<> \
inline void \
print_tens<tens>() \
{\
  cout << string;\
}

TENS_PRINTER(2, "Twenty")
TENS_PRINTER(3, "Thirty")
TENS_PRINTER(4, "Forty")
TENS_PRINTER(5, "Fifty")
TENS_PRINTER(6, "Sixty")
TENS_PRINTER(7, "Seventy")
TENS_PRINTER(8, "Eighty")
TENS_PRINTER(9, "Ninety")

#undef TENS_PRINTER

template<int I>
struct pretty_printer<false, I>
{
    static void print(){
        print_tens<(I - I%10)/10>();
        print_ones<(I%10)>();
    }
};

template<int I>
void pretty_print()
{
    pretty_printer<(I<20), I>::print();
}

template<int I>
inline void
BottlesOfBeer()
{
    pretty_print<I>();
    cout << " bottles of beer" ;
}

template<>
inline void
BottlesOfBeer<1>()
{
    pretty_print<1>();
    cout << " bottle of beer" ;
}

template<int I>
inline void
BottlesOfBeerOnTheWall()
{
    BottlesOfBeer<I>();
    cout << " on the wall";
}

template<int I>
inline void stanza()
{
    BottlesOfBeerOnTheWall<I>(); 
    cout << ",\n";
    BottlesOfBeer<I>(); 
    cout <<",\n";
}

template<int I>
inline void bridge()
{
    cout   << "Take one down, pass it around," << endl;
    BottlesOfBeerOnTheWall<I-1>();
    cout <<",\n";
}

template<>
inline void bridge<0>()
{
    cout << "Go to the store and buy some more," << endl;
    BottlesOfBeerOnTheWall<99>();
}

template<int I>
inline void verse()
{
    stanza<I>();
    bridge<I>();
}

template<int I>
inline void sing () 
{
    verse<I>();
    cout << endl;
    sing<I-1>();
} 


template<>
inline void sing<0> ()
{
    verse<0>();    
}

int main () {
  sing<99>();
}

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Alternative Versions

Version	Author	Date	Comments
meta programming	Arion Lei	04/20/05	2
hacking style	Tim Robinson	04/20/05	6
ob fuscated	Tapi (Paddy O'Brien)	08/11/05	2
object-oriented version	Tim Robinson	04/20/05	2
Preprocessor & self-include recursion	Chocapic	02/27/07	0
GUI version	Martyn Davies	05/28/05	0

Comments

cbuilder said on 06/28/05 09:15:39

If you compile with mingw - think of the following: add the parameter "-ftemplate-depth-999", otherwise you can't compile this (very hard ) source

Anonymous said on 06/28/05 09:15:48

If you compile with mingw - think of the following: add the parameter "-ftemplate-depth-999", otherwise you can't compile this (very hard ) source

Cari said on 07/15/05 12:27:37

Hmm... nice site but be more informative!

LifeIns said on 07/16/05 05:28:03

Nice site! Keep it updated more frequently!

BuyH said on 07/18/05 08:54:05

Very nice! Thank you for useful info.

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