Task: Bulls and cows_Player
C: #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

char *list;
const char *line = "--------+--------------------\n";
int len = 0;

int irand(int n)
{
	int r, rand_max = RAND_MAX - (RAND_MAX % n);
	do { r = rand(); } while(r >= rand_max);
	return r / (rand_max / n);
}

char* get_digits(int n, char *ret)
{
	int i, j;
	char d[] = "123456789";

	for (i = 0; i < n; i++) { 
		j = irand(9 - i);
		ret[i] = d[i + j];
		if (j) d[i + j] = d[i], d[i] = ret[i];
	}
	return ret;
}

#define MASK(x) (1 << (x - '1'))
int score(const char *digits, const char *guess, int *cow)
{
	int i, bits = 0, bull = *cow = 0;

	for (i = 0; guess[i] != '\0'; i++)
		if (guess[i] != digits[i])
			bits |= MASK(digits[i]);
		else ++bull;

	while (i--) *cow += ((bits & MASK(guess[i])) != 0);

	return bull;
}

void pick(int n, int got, int marker, char *buf)
{
	int i, bits = 1;
	if (got >= n)
		strcpy(list + (n + 1) * len++, buf);
	else
		for (i = 0; i < 9; i++, bits *= 2) {
			if ((marker & bits)) continue;
			buf[got] = i + '1';
			pick(n, got + 1, marker | bits, buf);
		}
}

void filter(const char *buf, int n, int bull, int cow)
{
	int i = 0, c;
	char *ptr = list;

	while (i < len) {
		if (score(ptr, buf, &c) != bull || c != cow)
			strcpy(ptr, list + --len * (n + 1));
		else
			ptr += n + 1, i++;
	}
}

void game(const char *tgt, char *buf)
{
	int i, p, bull, cow, n = strlen(tgt);

	for (i = 0, p = 1; i < n && (p *= 9 - i); i++);
	list = malloc(p * (n + 1));

	pick(n, 0, 0, buf);
	for (p = 1, bull = 0; n - bull; p++) {
		strcpy(buf, list + (n + 1) * irand(len));
		bull = score(tgt, buf, &cow);

		printf("Guess %2d| %s    (from: %d)\n"
			"Score   | %d bull, %d cow\n%s",
			p, buf, len, bull, cow, line);

		filter(buf, n, bull, cow);
	}
}

int main(int c, char **v)
{
	int n = c > 1 ? atoi(v[1]) : 4;

	char secret[10] = "", answer[10] = "";
	srand(time(0));

	printf("%sSecret  | %s\n%s", line, get_digits(n, secret), line);
	game(secret, answer);

	return 0;
}

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


using namespace std;


const unsigned int LEN = 4;


class CowsAndBulls_Player
{
public:
    CowsAndBulls_Player() { fillPool(); }
    void play() { secret = createSecret(); guess(); }

private:
    void guess()
    {
	pair<int, int> res; int cc = 1;
	cout << endl << " SECRET: " << secret << endl << "==============" << endl;
	cout << "+-----------+---------+--------+\n|   GUESS   |  BULLS  |  COWS  |\n+-----------+---------+--------+\n";
	while( true )
	{
	    string gs = gimmeANumber();
	    if( gs.empty() ) { cout << endl << "Something went wrong with the scoring..." << endl << "Cannot find an answer!" << endl; return; }
	    if( scoreIt( gs, res ) ) { cout << endl << "I found the secret number!" << endl << "It is: " << gs << endl; return; }
	    cout << "|    " << gs << "   |  " << setw( 3 ) << res.first << "    |  " << setw( 3 ) << res.second << "   |\n+-----------+---------+--------+\n";
	    clearPool( gs, res );
        }
    }

    void clearPool( string gs, pair<int, int>& r )
    {
	vector<string>::iterator pi = pool.begin();
	while( pi != pool.end() )
	{
	    if( removeIt( gs, ( *pi ), r ) ) pi = pool.erase( pi );
	    else  pi++;
	}
    }

    string gimmeANumber()
    {
	if( pool.empty() ) return "";
	return pool[rand() % pool.size()];
    }

    void fillPool()
    {
	for( int x = 1234; x < 9877; x++ )
	{
	    ostringstream oss; oss << x;
	    if( check( oss.str() ) ) pool.push_back( oss.str() );
	}
    }

    bool check( string s )
    {
	for( string::iterator si = s.begin(); si != s.end(); si++ )
	{
	    if( ( *si ) == '0' ) return false;
	    if( count( s.begin(), s.end(), ( *si ) ) > 1 ) return false;
	}
	return true;
    }

    bool removeIt( string gs, string ts, pair<int, int>& res )
    {
	pair<int, int> tp; getScore( gs, ts, tp );
	return tp != res;
    }

    bool scoreIt( string gs, pair<int, int>& res )
    {
	getScore( gs, secret, res );
	return res.first == LEN;
    }

    void getScore( string gs, string st, pair<int, int>& pr )
    {
	pr.first = pr.second = 0;
	for( unsigned int ui = 0; ui < LEN; ui++ )
	{
	    if( gs[ui] == st[ui] ) pr.first++;
	    else
	    {
		for( unsigned int vi = 0; vi < LEN; vi++ )
		    if( gs[ui] == st[vi] ) pr.second++;
	    }
	}
    }

    string createSecret()
    {
	string n = "123456789", rs = "";
	while( rs.length() < LEN )
	{
	    int r = rand() % n.length();
	    rs += n[r]; n.erase( r, 1 );
	}
	return rs;
    }

    string secret;
    vector<string> pool;
};

int main( int argc, char* argv[] )
{
    srand( static_cast<unsigned int>( time( NULL ) ) ); CowsAndBulls_Player cb;
    cb.play(); cout << endl << endl;
    return system( "pause" );
}