BigInteger之高精度乘法

 1 BigInteger operator * (const BigInteger& b){
 2         BigInteger c,d;
 3         c.s.clear();
 4         d.s.clear();
 5         int rst;
 6         for(int i=0;i<s.size();i++){
 7             for(int j = 0;j<b.s.size();j++){
 8                 stringstream ss;
 9                 string str;
10                 rst = s[i]*b.s[j];
11                 ss<<rst;
12                 ss>>str;
13                 str+=func((i+j)*WIDTH);
14                 d = str;
15                 c = c+d;
16             }
17         }
18         return c;
19     }

 1 #include <iostream>
 2 #include <cstring>
 3 #include <vector>
 4 #include<stdio.h>
 5 #include<sstream>
 6 using namespace std;
 7 string func(int n){
 8     string s;
 9     for(int i=0;i<n;i++)
10         s+="0";
11     return s;
12 }
13 struct BigInteger {
14     static const int BASE = 10000;
15     static const int WIDTH = 4;
16     vector<int> s;
17     BigInteger (long long num = 0){*this = num;}
18     BigInteger operator = (long long num){
19         s.clear();
20         do{
21             s.push_back(num % BASE);
22             num/= BASE;
23         }while(num>0);
24         return *this;
25     }
26     BigInteger operator = (const string& str) {
27         s.clear();
28         int x,len = (str.length()-1)/WIDTH +1;
29         for(int i =0; i<len; i++) {
30             int end = str.length() - i*WIDTH;
31             int start = max(0,end-WIDTH);
32             sscanf(str.substr(start,end-start).c_str(),"%d",&x);
33             s.push_back(x);
34         }
35         return *this;
36     }
37     BigInteger operator + (const BigInteger& b){
38         BigInteger c;
39         c.s.clear();
40         for(int i=0,g=0;;i++){
41             if(g==0&& i>=s.size()&&i>=b.s.size()) break;
42             int x = g;
43             if(i< s.size())x+=s[i];
44             if(i<b.s.size())x+=b.s[i];
45             c.s.push_back(x%BASE);
46             g = x/BASE;
47         }
48         return c;
49     }
50     BigInteger operator * (const BigInteger& b){
51         BigInteger c,d;
52         c.s.clear();
53         d.s.clear();
54         int rst;
55         for(int i=0;i<s.size();i++){
56             for(int j = 0;j<b.s.size();j++){
57                 stringstream ss;
58                 string str;
59                 rst = s[i]*b.s[j];
60                 ss<<rst;
61                 ss>>str;
62                 str+=func((i+j)*WIDTH);
63                 d = str;
64                 c = c+d;
65             }
66         }
67         return c;
68     }
69 };
70 
71 ostream& operator << (ostream &out,const BigInteger& x) {
72     BigInteger c;
73     c = x;
74   while(c.s.end()-1!=c.s.begin()){
75         if(c.s.back()==0) c.s.pop_back();
76        else break;
77    }
78     out<<c.s.back();
79     for(int i=c.s.size()-2; i>=0; i--) {
80         char buf[20];
81         sprintf(buf,"%0*d",BigInteger::WIDTH,c.s[i]);
82         for(int j=0; j<strlen(buf); j++)
83             out<<buf[j];
84     }
85     return out;
86 }
87 istream& operator >> (istream &in,BigInteger& x){
88     string s;
89     if(!(in>>s))return in;
90     x = s;
91     return in;
92 }
93 
94 int main() {
95     BigInteger a,b;
96     cin>>a>>b;
97     cout<<a*b<<endl;
98     return 0;
99 }