321未来可期 2022-03-20 22:16 采纳率: 100%

c++编一程序，求50和100的阶乘（利用数组保存结果中的每一位数字）

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• _GX_ 2022-03-21 03:16
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``````#include <iostream>
#include <string>
#include <iterator>
#include <vector>

class BigInt
{
public:
BigInt(unsigned int n = 0)
{
if (n == 0)
_data.push_back('0');
else
{
while (n)
{
_data.push_back(n % 10 + '0');
n /= 10;
}
}
}

BigInt(const std::string &s) : _data(s.rbegin(), s.rend()) {}

BigInt &operator+=(const BigInt &other);
BigInt &operator*=(const BigInt &other);

BigInt operator+(const BigInt &other) const
{
BigInt t = *this;
t += other;
return t;
}

BigInt operator*(const BigInt &other) const
{
BigInt t = *this;
t *= other;
return t;
}

private:
std::string _data;

friend std::istream &operator>>(std::istream &is, BigInt &a);
friend std::ostream &operator<<(std::ostream &os, const BigInt &a);
};

BigInt &BigInt::operator+=(const BigInt &other)
{
int carry = 0;
std::string::iterator itr1 = _data.begin();
std::string::const_iterator itr2 = other._data.begin();
while (itr1 != _data.end() && itr2 != other._data.end())
{
int a = *itr1 - '0';
int b = *itr2 - '0';
int c = a + b + carry;
carry = c / 10;
c %= 10;
*itr1 = c + '0';
++itr1;
++itr2;
}
while (itr1 != _data.end())
{
int a = *itr1 - '0' + carry;
carry = a / 10;
a %= 10;
*itr1 = a + '0';
++itr1;
}
while (itr2 != other._data.end())
{
int a = *itr2 - '0' + carry;
carry = a / 10;
a %= 10;
_data.push_back(a + '0');
++itr2;
}
if (carry > 0)
_data.push_back(carry + '0');
return *this;
}

BigInt &BigInt::operator*=(const BigInt &other)
{
BigInt r;
for (std::size_t i = 0; i < other._data.size(); i++)
{
int x = other._data[i] - '0';
int carry = 0;
BigInt t = *this;
for (std::string::iterator itr = t._data.begin(); itr != t._data.end(); ++itr)
{
int y = *itr - '0';
int a = x * y + carry;
*itr = a % 10 + '0';
carry = a / 10;
}
if (carry > 0)
t._data.push_back(carry + '0');
if (i > 0)
{
std::string zeros(i, '0');
t._data.insert(t._data.begin(), zeros.begin(), zeros.end());
}
r += t;
}
*this = r;
return *this;
}

std::istream &operator>>(std::istream &is, BigInt &a)
{
std::string s;
is >> s;
a = s;
return is;
}

std::ostream &operator<<(std::ostream &os, const BigInt &a)
{
std::copy(a._data.rbegin(), a._data.rend(), std::ostream_iterator<char>(os));
return os;
}

BigInt factorial(int n)
{
BigInt r = 1;
for (int i = 1; i <= n; i++)
r *= i;
return r;
}

int main()
{
std::cout << "50! = " << factorial(50) << std::endl;
std::cout << "100! = " << factorial(100) << std::endl;
return 0;
}
``````
``````\$ g++ -Wall main.cpp
\$ ./a.out
50! = 30414093201713378043612608166064768844377641568960512000000000000
100! = 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
``````
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• 系统已结题 3月29日
• 已采纳回答 3月21日
• 创建了问题 3月20日

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