blob: 98f12a38b81ac7c5355927f3ff8907ef0d54c163 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
// 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;
}
//]
|
