40 lines
1.2 KiB
C++
40 lines
1.2 KiB
C++
|
|
// Copyright (C) 2008-2018 Lorenzo Caminiti
|
|
// Distributed under the Boost Software License, Version 1.0 (see accompanying
|
|
// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
|
|
// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
|
|
|
|
//[n1962_factorial
|
|
#include <boost/contract.hpp>
|
|
#include <cassert>
|
|
|
|
int factorial(int n) {
|
|
int result;
|
|
boost::contract::check c = boost::contract::function()
|
|
.precondition([&] {
|
|
BOOST_CONTRACT_ASSERT(n >= 0); // Non-negative natural number.
|
|
BOOST_CONTRACT_ASSERT(n <= 12); // Max function input.
|
|
})
|
|
.postcondition([&] {
|
|
BOOST_CONTRACT_ASSERT(result >= 1);
|
|
if(n < 2) { // Select assertion.
|
|
BOOST_CONTRACT_ASSERT(result == 1);
|
|
} else {
|
|
// Assertions automatically disabled in other assertions.
|
|
// Therefore, this postcondition can recursively call the
|
|
// function without causing infinite recursion.
|
|
BOOST_CONTRACT_ASSERT_AUDIT(n * factorial(n - 1));
|
|
}
|
|
})
|
|
;
|
|
|
|
return n < 2 ? (result = 1) : (result = n * factorial(n - 1));
|
|
}
|
|
|
|
int main() {
|
|
assert(factorial(4) == 24);
|
|
return 0;
|
|
}
|
|
//]
|
|
|