首先感谢刘汝佳所著的《算法竞赛入门经典》。
众所周知，C++中储存能力最大的unsigned long long 也是有着一个上限，如果我们想计算非常大的整数时，就不知所措了，所以，我写了一个高精度类，允许大整数的四则运算
这个类利用字符串进行输入输出，并利用数组进行储存与处理，通过模拟四则运算，可以计算很大的整数的加减乘除比大小。
支持负数，前导零，支持字符串、整型赋值，支持流输入输出
贴上我的代码：
#include<string> #include<iostream> #include<iosfwd> #include<cmath> #include<cstring> #include<stdlib.h> #include<stdio.h> #include<cstring> #define MAX_L 2005 //最大长度，可以修改 using namespace std;class bign { public:int len, s[MAX_L];//数的长度，记录数组 //构造函数 bign();bign(const char*);bign(int);bool sign;//符号 1正数 0负数string toStr() const;//转化为字符串，主要是便于输出friend istream& operator>>(istream &,bign &);//重载输入流friend ostream& operator<<(ostream &,bign &);//重载输出流 //重载复制bign operator=(const char*);bign operator=(int);bign operator=(const string); //重载各种比较bool operator>(const bign &) const;bool operator>=(const bign &) const;bool operator<(const bign &) const;bool operator<=(const bign &) const;bool operator==(const bign &) const;bool operator!=(const bign &) const; //重载四则运算bign operator+(const bign &) const;bign operator++();bign operator++(int);bign operator+=(const bign&);bign operator-(const bign &) const;bign operator--();bign operator--(int);bign operator-=(const bign&);bign operator*(const bign &)const;bign operator*(const int num)const;bign operator*=(const bign&);bign operator/(const bign&)const;bign operator/=(const bign&); //四则运算的衍生运算bign operator%(const bign&)const;//取模（余数）bign factorial()const;//阶乘bign Sqrt()const;//整数开根（向下取整）bign pow(const bign&)const;//次方 //一些乱乱的函数void clean();~bign(); }; #define max(a,b) a>b ? a : b #define min(a,b) a<b ? a : bbign::bign() {memset(s, 0, sizeof(s));len = 1;sign = 1; }bign::bign(const char *num) {*this = num; }bign::bign(int num) {*this = num; }string bign::toStr() const {string res;res = "";for (int i = 0; i < len; i++)res = (char)(s[i] + '0') + res;if (res == "")res = "0";if (!sign&&res != "0")res = "-" + res;return res; }istream &operator>>(istream &in, bign &num) {string str;in>>str;num=str;return in; }ostream &operator<<(ostream &out, bign &num) {out<<num.toStr();return out; }bign bign::operator=(const char *num) {memset(s, 0, sizeof(s));char a[MAX_L] = "";if (num[0] != '-')strcpy(a, num);elsefor (int i = 1; i < strlen(num); i++)a[i - 1] = num[i];sign = !(num[0] == '-');len = strlen(a);for (int i = 0; i < strlen(a); i++)s[i] = a[len - i - 1] - 48;return *this; }bign bign::operator=(int num) {char temp[MAX_L];sprintf(temp, "%d", num);*this = temp;return *this; }bign bign::operator=(const string num) {const char *tmp;tmp = num.c_str();*this = tmp;return *this; }bool bign::operator<(const bign &num) const {if (sign^num.sign)return num.sign;if (len != num.len)return len < num.len;for (int i = len - 1; i >= 0; i--)if (s[i] != num.s[i])return sign ? (s[i] < num.s[i]) : (!(s[i] < num.s[i]));return !sign; }bool bign::operator>(const bign&num)const {return num < *this; }bool bign::operator<=(const bign&num)const {return !(*this>num); }bool bign::operator>=(const bign&num)const {return !(*this<num); }bool bign::operator!=(const bign&num)const {return *this > num || *this < num; }bool bign::operator==(const bign&num)const {return !(num != *this); }bign bign::operator+(const bign &num) const {if (sign^num.sign){bign tmp = sign ? num : *this;tmp.sign = 1;return sign ? *this - tmp : num - tmp;}bign result;result.len = 0;int temp = 0;for (int i = 0; temp || i < (max(len, num.len)); i++){int t = s[i] + num.s[i] + temp;result.s[result.len++] = t % 10;temp = t / 10;}result.sign = sign;return result; }bign bign::operator++() {*this = *this + 1;return *this; }bign bign::operator++(int) {bign old = *this;++(*this);return old; }bign bign::operator+=(const bign &num) {*this = *this + num;return *this; }bign bign::operator-(const bign &num) const {bign b=num,a=*this;if (!num.sign && !sign){b.sign=1;a.sign=1;return b-a;}if (!b.sign){b.sign=1;return a+b;}if (!a.sign){a.sign=1;b=bign(0)-(a+b);return b;}if (a<b){bign c=(b-a);c.sign=false;return c;}bign result;result.len = 0;for (int i = 0, g = 0; i < a.len; i++){int x = a.s[i] - g;if (i < b.len) x -= b.s[i];if (x >= 0) g = 0;else{g = 1;x += 10;}result.s[result.len++] = x;}result.clean();return result; }bign bign::operator * (const bign &num)const {bign result;result.len = len + num.len;for (int i = 0; i < len; i++)for (int j = 0; j < num.len; j++)result.s[i + j] += s[i] * num.s[j];for (int i = 0; i < result.len; i++){result.s[i + 1] += result.s[i] / 10;result.s[i] %= 10;}result.clean();result.sign = !(sign^num.sign);return result; }bign bign::operator*(const int num)const {bign x = num;bign z = *this;return x*z; } bign bign::operator*=(const bign&num) {*this = *this * num;return *this; }bign bign::operator /(const bign&num)const {bign ans;ans.len = len - num.len + 1;if (ans.len < 0){ans.len = 1;return ans;}bign divisor = *this, divid = num;divisor.sign = divid.sign = 1;int k = ans.len - 1;int j = len - 1;while (k >= 0){while (divisor.s[j] == 0) j--;if (k > j) k = j;char z[MAX_L];memset(z, 0, sizeof(z));for (int i = j; i >= k; i--)z[j - i] = divisor.s[i] + '0';bign dividend = z;if (dividend < divid) { k--; continue; }int key = 0;while (divid*key <= dividend) key++;key--;ans.s[k] = key;bign temp = divid*key;for (int i = 0; i < k; i++)temp = temp * 10;divisor = divisor - temp;k--;}ans.clean();ans.sign = !(sign^num.sign);return ans; }bign bign::operator/=(const bign&num) {*this = *this / num;return *this; }bign bign::operator%(const bign& num)const {bign a = *this, b = num;a.sign = b.sign = 1;bign result, temp = a / b*b;result = a - temp;result.sign = sign;return result; }bign bign::pow(const bign& num)const {bign result = 1;for (bign i = 0; i < num; i++)result = result*(*this);return result; }bign bign::factorial()const {bign result = 1;for (bign i = 1; i <= *this; i++)result *= i;return result; }void bign::clean() {if (len == 0) len++;while (len > 1 && s[len - 1] == '\0')len--; }bign bign::Sqrt()const {if(*this<0)return -1;if(*this<=1)return *this;bign l=0,r=*this,mid;while(r-l>1){mid=(l+r)/2;if(mid*mid>*this)r=mid;elsel=mid;}return l; }bign::~bign() { }bign num0,num1,res;int main() {num0 = 1, num1 = 2;res=num0-num1;cout << res << endl;return 0; }
