高精度封装大礼包

struct bign{  
    int d[50], len;  

    void clean() { while(len > 1 && !d[len-1]) len--; }  

    bign()          { memset(d, 0, sizeof(d)); len = 1; }  
    bign(int num)   { *this = num; }   
    bign(char* num) { *this = num; }  
    bign operator = (const char* num){  
        memset(d, 0, sizeof(d)); len = strlen(num);  
        for(int i = 0; i < len; i++) d[i] = num[len-1-i] - '0';  
        clean();  
        return *this;  
    }  
    bign operator = (int num){  
        char s[20]; sprintf(s, "%d", num);  
        *this = s;  
        return *this;  
    }  

    bign operator + (const bign& b){  
        bign c = *this; int i;  
        for (i = 0; i < b.len; i++){  
            c.d[i] += b.d[i];  
            if (c.d[i] > 9) c.d[i]%=10, c.d[i+1]++;  
        }  
        while (c.d[i] > 9) c.d[i++]%=10, c.d[i]++;  
        c.len = max(len, b.len);  
        if (c.d[i] && c.len <= i) c.len = i+1;  
        return c;  
    }  
    bign operator - (const bign& b){  
        bign c = *this; int i;  
        for (i = 0; i < b.len; i++){  
            c.d[i] -= b.d[i];  
            if (c.d[i] < 0) c.d[i]+=10, c.d[i+1]--;  
        }  
        while (c.d[i] < 0) c.d[i++]+=10, c.d[i]--;  
        c.clean();  
        return c;  
    }  
    bign operator * (const bign& b)const{  
        int i, j; bign c; c.len = len + b.len;   
        for(j = 0; j < b.len; j++) for(i = 0; i < len; i++)   
            c.d[i+j] += d[i] * b.d[j];  
        for(i = 0; i < c.len-1; i++)  
            c.d[i+1] += c.d[i]/10, c.d[i] %= 10;  
        c.clean();  
        return c;  
    }  
    bign operator / (const bign& b){  
        int i, j;  
        bign c = *this, a = 0;  
        for (i = len - 1; i >= 0; i--)  
        {  
            a = a*10 + d[i];  
            for (j = 0; j < 10; j++) if (a < b*(j+1)) break;  
            c.d[i] = j;  
            a = a - b*j;  
        }  
        c.clean();  
        return c;  
    }  
    bign operator % (const bign& b){  
        int i, j;  
        bign a = 0;  
        for (i = len - 1; i >= 0; i--)  
        {  
            a = a*10 + d[i];  
            for (j = 0; j < 10; j++) if (a < b*(j+1)) break;  
            a = a - b*j;  
        }  
        return a;  
    }  
    bign operator += (const bign& b){  
        *this = *this + b;  
        return *this;  
    }  

    bool operator <(const bign& b) const{  
        if(len != b.len) return len < b.len;  
        for(int i = len-1; i >= 0; i--)  
            if(d[i] != b.d[i]) return d[i] < b.d[i];  
        return false;  
    }  
    bool operator >(const bign& b) const{return b < *this;}  
    bool operator<=(const bign& b) const{return !(b < *this);}  
    bool operator>=(const bign& b) const{return !(*this < b);}  
    bool operator!=(const bign& b) const{return b < *this || *this < b;}  
    bool operator==(const bign& b) const{return !(b < *this) && !(b > *this);}  

    string str() const{  
        char s[maxn]={};  
        for(int i = 0; i < len; i++) s[len-1-i] = d[i]+'0';  
        return s;  
    }  
};  
istream& operator >> (istream& in, bign& x)  
{  
    string s;  
    in >> s;  
    x = s.c_str();  
    return in;  
}  

ostream& operator << (ostream& out, const bign& x)  
{  
    out << x.str();  
    return out;  
}

加

string add(string a,string b){
    if(a.size() > b.size()) swap(a,b);
    b.insert(b.begin(),'0');
    int t = 0;
    for(int i = b.size()-1,j = a.size()-1;i>=0;i--,j--){
        int cur;
        if(j>=0) cur = (a[j]-'0') + (b[i]-'0') + t;
        else cur = (b[i] - '0') +t;
        b[i] = (cur%10) + '0';
        t = cur/10;
    }
    int idx = b.find_first_not_of('0');
    return idx != -1? b.substr(idx): "0";
}

减

string sub(string a,string b){
    //a大b小
    int t = 0;
    for(int i = a.size()-1,j = b.size()-1;i>=0;i--,j--){
        int up = 0,down = 0;
        up = (a[i]-'0') + t; t = 0;
        if(j>=0) down = (b[j]-'0');
        if(up < down) up+=10,t = -1;
        int cur = up-down;
        a[i] = cur+&#39;0&#39;;
    }
    int idx = a.find_first_not_of(&#39;0&#39;);
    return idx != -1? a.substr(idx) : "0";
}

乘（高精度*低精度）

string mul(string a,ll b){
    string c = "";
    ll t = 0;
    for(int i = a.size()-1;i>=0 || t;i--){
        if(i>=0) t += (a[i]-'0')*b;
        c += (t%10) +'0';
        t/=10;
    }
    reverse(c.begin(),c.end());
    return c;
}

除（高精度/低精度）

返回商的整数部分

string div(string a,ll b){
    string c = "";
    ll cur = 0;
    for(int i = 0;i<a.size();i++){
        cur = cur*10 + (a[i]-&#39;0&#39;);
        c += to_string(cur/b);
        cur %= b;
    }
    int idx = c.find_first_not_of(&#39;0&#39;);
    return idx!=-1 ? c.substr(idx) : "0";
}

比较大小

bool cmp(string a,string b){
    int idx1 = a.find_first_not_of('0'),idx2 = b.find_first_not_of('0');
    a = idx1!=-1? a.substr(idx1) : "0";
    b = idx2!=-1? b.substr(idx2) : "0";
    if(a.size() != b.size()) return a.size() >= b.size();
    return a>=b;
}

所有

#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <vector>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#define PI acos(-1)
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const ll maxn = 1e6+10;
double eps = 1e-8;

bool cmp(string a,string b){
    int idx1 = a.find_first_not_of(&#39;0&#39;),idx2 = b.find_first_not_of(&#39;0&#39;);
    a = idx1!=-1? a.substr(idx1) : "0";
    b = idx2!=-1? b.substr(idx2) : "0";
    if(a.size() != b.size()) return a.size() >= b.size();
    return a>=b;
}

string add(string a,string b){
    if(a.size() > b.size()) swap(a,b);
    b.insert(b.begin(),&#39;0&#39;);
    int t = 0;
    for(int i = b.size()-1,j = a.size()-1;i>=0;i--,j--){
        int cur;
        if(j>=0) cur = (a[j]-&#39;0&#39;) + (b[i]-&#39;0&#39;) + t;
        else cur = (b[i] - &#39;0&#39;) +t;
        b[i] = (cur%10) + &#39;0&#39;;
        t = cur/10;
    }
    int idx = b.find_first_not_of(&#39;0&#39;);
    return idx != -1? b.substr(idx): "0";
}

string sub(string a,string b){
    //a大b小
    int t = 0;
    for(int i = a.size()-1,j = b.size()-1;i>=0;i--,j--){
        int up = 0,down = 0;
        up = (a[i]-&#39;0&#39;) + t; t = 0;
        if(j>=0) down = (b[j]-&#39;0&#39;);
        if(up < down) up+=10,t = -1;
        int cur = up-down;
        a[i] = cur+&#39;0&#39;;
    }
    int idx = a.find_first_not_of(&#39;0&#39;);
    return idx != -1? a.substr(idx) : "0";
}

string mul(string a,ll b){
    string c = "";
    ll t = 0;
    for(int i = a.size()-1;i>=0 || t;i--){
        if(i>=0) t += (a[i]-&#39;0&#39;)*b;
        c += (t%10) +&#39;0&#39;;
        t/=10;
    }
    reverse(c.begin(),c.end());
    return c;
}
string divbb(string a,string b,int len){
    //未验证
    string c = "";int tag = 1;
    for(int i = 1;i<=len;i++){
        int cnt = 0;
        while(cmp(a,b)){
            cnt++;
            a = sub(a,b);
        }
        c += to_string(cnt);
        if(tag) c+=&#39;.&#39;;tag = 0;
        a += &#39;0&#39;;
    }
    return c;
}

string div(string a,ll b){
    string c = "";
    ll cur = 0;
    for(int i = 0;i<a.size();i++){
        cur = cur*10 + (a[i]-&#39;0&#39;);
        c += to_string(cur/b);
        cur %= b;
    }
    int idx = c.find_first_not_of(&#39;0&#39;);
    return idx!=-1 ? c.substr(idx) : "0";
}

int main(){
    string a;ll b;
    cin>>a>>b;
    cout<<mul(a,b)<<endl;
    return 0;
}