 C++: Bulls and Cows This is an old game played with pencil and paper that was later implemented on computer.

The task is for the program to create a four digit random number from the digits 1 to 9, without duplication. The program should ask for guesses to this number, reject guesses that are malformed, then print the score for the guess.

The score is computed as:

1. The player wins if the guess is the same as the randomly chosen number, and the program ends.
2. A score of one bull is accumulated for each digit in the guess that equals the corresponding digit in the randomly chosen initial number.
3. A score of one cow is accumulated for each digit in the guess that also appears in the randomly chosen number, but in the wrong position.

#include <iostream>
#include <string>
#include <algorithm>
#include <cstdlib>

bool contains_duplicates(std::string s)
{
std::sort(s.begin(), s.end());
}

void game()
{
typedef std::string::size_type index;

std::string symbols = "0123456789";
unsigned int const selection_length = 4;

std::random_shuffle(symbols.begin(), symbols.end());
std::string selection = symbols.substr(0, selection_length);
std::string guess;
while (std::cout << "Your guess? ", std::getline(std::cin, guess))
{
if (guess.length() != selection_length
|| guess.find_first_not_of(symbols) != std::string::npos
|| contains_duplicates(guess))
{
std::cout << guess << " is not a valid guess!";
continue;
}

unsigned int bulls = 0;
unsigned int cows = 0;
for (index i = 0; i != selection_length; ++i)
{
index pos = selection.find(guess[i]);
if (pos == i)
++bulls;
else if (pos != std::string::npos)
++cows;
}
std::cout << bulls << " bulls, " << cows << " cows.\n";
if (bulls == selection_length)
{
std::cout << "Congratulations! You have won!\n";
return;
}
}
std::cerr << "Oops! Something went wrong with input, or you've entered end-of-file!\nExiting ...\n";
std::exit(EXIT_FAILURE);
}

int main()
{
std::cout << "Welcome to bulls and cows!\nDo you want to play? ";
while (true)
{
while (true)
{
{
std::cout << "I can't get an answer. Exiting.\n";
return EXIT_FAILURE;
}
break;
{
std::cout << "Ok. Goodbye.\n";
return EXIT_SUCCESS;
}
}
game();
std::cout << "Another game? ";
}
}

SOURCE

Content is available under GNU Free Documentation License 1.2.