Task: Set puzzle
C: #include <stdio.h>
#include <stdlib.h>

char *names[4][3] = {
	{ "red", "green", "purple" },
	{ "oval", "squiggle", "diamond" },
	{ "one", "two", "three" },
	{ "solid", "open", "striped" }
};

int set[81][81];

void init_sets(void)
{
	int i, j, t, a, b;
	for (i = 0; i < 81; i++) {
		for (j = 0; j < 81; j++) {
			for (t = 27; t; t /= 3) {
				a = (i / t) % 3;
				b = (j / t) % 3;
				set[i][j] += t * (a == b ? a : 3 - a - b);
			}
		}
	}
}

void deal(int *out, int n)
{
	int i, j, t, c[81];
	for (i = 0; i < 81; i++) c[i] = i;
	for (i = 0; i < n; i++) {
		j = i + (rand() % (81 - i));
		t = c[i], c[i] = out[i] = c[j], c[j] = t;
	}
}

int get_sets(int *cards, int n, int sets[][3])
{
	int i, j, k, s = 0;
	for (i = 0; i < n; i++) {
		for (j = i + 1; j < n; j++) {
			for (k = j + 1; k < n; k++) {
				if (set[cards[i]][cards[j]] == cards[k])
					sets[s][0] = i,
					sets[s][1] = j,
					sets[s][2] = k,
					s++;
			}
		}
	}

	return s;
}

void show_card(int c)
{
	int i, t;
	for (i = 0, t = 27; t; i++, t /= 3)
		printf("%9s", names[i][(c/t)%3]);
	putchar('\n');
}

void deal_sets(int ncard, int nset)
{
	int c[81];
	int csets[81][3]; 
	int i, j, s;

	do deal(c, ncard); while ((s = get_sets(c, ncard, csets)) != nset);

	printf("dealt %d cards\n", ncard);
	for (i = 0; i < ncard; i++) {
		printf("%2d:", i);
		show_card(c[i]);
	}
	printf("\nsets:\n");

	for (i = 0; i < s; i++) {
		for (j = 0; j < 3; j++) {
			printf("%2d:", csets[i][j]);
			show_card(c[csets[i][j]]);
		}
		putchar('\n');
	}
}

int main(void)
{
	init_sets();
	deal_sets(9, 4);

	while (1) deal_sets(12, 6);

	return 0;
}

C++: #include <time.h>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>

enum color {
    red, green, purple 
};
enum symbol {
    oval, squiggle, diamond 
};
enum number {
    one, two, three 
};
enum shading {
    solid, open, striped 
};
class card {
public:
    card( color c, symbol s, number n, shading h ) {
        clr = c; smb = s; nbr = n; shd = h;
    }
    color getColor() { 
        return clr;
    }
    symbol getSymbol() { 
        return smb; 
    }
    number getNumber() {
        return nbr; 
    }
    shading getShading() {
        return shd;
    }
    std::string toString() {
        std::string str = "[";
        str += clr == red ? "red " : clr == green ? "green " : "purple ";
        str += nbr == one ? "one " : nbr == two ? "two " : "three ";
        str += smb == oval ? "oval " : smb == squiggle ? "squiggle " : "diamond ";
        str += shd == solid ? "solid" : shd == open ? "open" : "striped";
        return str + "]";
    }
private:
    color    clr;
    symbol   smb;
    number   nbr;
    shading  shd;
};
typedef struct {
    std::vector<size_t> index;
} set;
class setPuzzle {
public:
    setPuzzle() {
        for( size_t c = red; c <= purple; c++ ) {
            for( size_t s = oval; s <= diamond; s++ ) {
                for( size_t n = one; n <= three; n++ ) {
                    for( size_t h = solid; h <= striped; h++ ) {
                        card crd( static_cast<color>  ( c ), 
                                  static_cast<symbol> ( s ), 
                                  static_cast<number> ( n ), 
                                  static_cast<shading>( h ) );
                        _cards.push_back( crd );
                    }
                }
            }
        }
    }
    void create( size_t countCards, size_t countSets, std::vector<card>& cards, std::vector<set>& sets ) {
        while( true ) {
            sets.clear();
            cards.clear();
            std::random_shuffle( _cards.begin(), _cards.end() );
            for( size_t f = 0; f < countCards; f++ ) {
                cards.push_back( _cards.at( f ) );
            }
            for( size_t c1 = 0; c1 < cards.size() - 2; c1++ ) {
                for( size_t c2 = c1 + 1; c2 < cards.size() - 1; c2++ ) {
                    for( size_t c3 = c2 + 1; c3 < cards.size(); c3++ ) {
                        if( testSet( &cards.at( c1 ), &cards.at( c2 ), &cards.at( c3 ) ) ) {
                            set s;
                            s.index.push_back( c1 ); s.index.push_back( c2 ); s.index.push_back( c3 );
                            sets.push_back( s );
                        }
                    }
                }
            }
            if( sets.size() == countSets ) return;
        }
    }
private:
    bool testSet( card* c1, card* c2, card* c3 ) {
        int
        c = ( c1->getColor()   + c2->getColor()   + c3->getColor()   ) % 3,
        s = ( c1->getSymbol()  + c2->getSymbol()  + c3->getSymbol()  ) % 3,
        n = ( c1->getNumber()  + c2->getNumber()  + c3->getNumber()  ) % 3,
        h = ( c1->getShading() + c2->getShading() + c3->getShading() ) % 3;
        return !( c + s + n + h );
    }
    std::vector<card> _cards;
};
void displayCardsSets( std::vector<card>& cards, std::vector<set>& sets ) {
    size_t cnt = 1;
    std::cout << " ** DEALT " << cards.size() << " CARDS: **\n";
    for( std::vector<card>::iterator i = cards.begin(); i != cards.end(); i++ ) {
        std::cout << std::setw( 2 ) << cnt++ << ": " << ( *i ).toString() << "\n";
    }
    std::cout << "\n ** CONTAINING " << sets.size() << " SETS: **\n";
    for( std::vector<set>::iterator i = sets.begin(); i != sets.end(); i++ ) {
        for( size_t j = 0; j < ( *i ).index.size(); j++ ) {
            std::cout << " " << std::setiosflags( std::ios::left ) << std::setw( 34 ) 
                      << cards.at( ( *i ).index.at( j ) ).toString() << " : "
                      << std::resetiosflags( std::ios::left ) << std::setw( 2 ) << ( *i ).index.at( j ) + 1 << "\n";
        }
        std::cout << "\n";
    }
    std::cout << "\n\n";
}
int main( int argc, char* argv[] ) {
    srand( static_cast<unsigned>( time( NULL ) ) );
    setPuzzle p;
    std::vector<card> v9, v12;
    std::vector<set>  s4, s6;
    p.create(  9, 4,  v9, s4 );
    p.create( 12, 6, v12, s6 );
    displayCardsSets(  v9, s4 );
    displayCardsSets( v12, s6 );
    return 0;
}