普通算法：参考自：http://wangxiaosu0501.blog.163.com/blog/static/11565259920110495415730/

#include <iostream> #include <string> #include <vector> using namespace std; vector<int> multiply(vector<int> v1,vector<int> v2); int main(){ vector<int> v1; vector<int> v2; string str1; string str2; cout<<"type in 2 bigNumber:"<<endl; cin >> str1 >> str2; for(int i = str1.size()-1;i>=0; i--) v1.push_back(str1[i] - '0'); for(int i = str2.size()-1;i>=0; i--) v2.push_back(str2[i]-'0'); vector<int> v = multiply(v1,v2); for(int i = v.size()-1;i>=0;--i) cout<<v[i]; cout<<endl; return 0; } vector<int> multiply(vector<int> v1,vector<int> v2){ int m = v1.size(); int n = v2.size(); vector<int> v(m*n+2,0);//Constructor! for(int i = 0; i != v2.size(); i++){ int k = i; for(int j = 0;j != v1.size(); j++) v[k++] += v2[i]*v1[j]; } for(vector<int>::iterator i = v.begin(); i!=v.end();i++) if(*i>9){ (*(i+1)) += (*i)/10; (*i) %= 10; } vector<int>::iterator i = (--v.end()); while(*i == 0){ v.pop_back(); i = (--v.end()); } return v; }

以下代码参考自：http://blog.csdn.net/sophie_wise8/article/details/7669116

#include <iostream>
#include <sstream>
#include <string>
using namespace std;
int string_to_num(string k){
   int back;
   stringstream instr(k);
   instr>>back;
   return back;
}
string num_to_string(int intValue){
   string result;
   stringstream stream;
   stream<<intValue;
   stream>>result;
   return result;
}
string stringBeforeZero(string str,int s){
   for(int i = 0; i < s; i++){
     str.insert(0,"0");
   }
   return str;
}
string stringAddstring(string str1,string str2){
   if(str1.size() > str2.size()){
     str2 = stringBeforeZero(str2,str1.size()-str2.size());
   }else if(str1.size() < str2.size()){
     str1 = stringBeforeZero(str1,str2.size()-str1.size());
   }
   string result;
   int flag = 0;
   for(int i = str1.size()-1; i >= 0; i--){
      int c = (str1[i]-'0')+(str2[i]-'0')+flag;
	  flag = c/10;
	  c %= 10;
	  result.insert(0,num_to_string(c));
   }
   if(0!=flag){
      result.insert(0,num_to_string(flag));
   }
   return result;
}
string stringSubtractstring(string str1,string str2){
   while('0' == str1[0] && str1.size() > 1){
     str1 = str1.substr(1,str1.size()-1);
   }
   while('0' == str2[0]&&str2.size() > 1){
     str2 = str2.substr(1,str2.size()-1);
   }
   if(str1.size() > str2.size()){
     str2 = stringBeforeZero(str2,str1.size()-str2.size());
   }
   string result;
   for(int i = str1.size() - 1;i >= 0;i--){
      int c= (str1[i] - '0')-(str2[i] - '0');
	  if(c < 0){
	     c += 10;
		 int prePos = i - 1;
		 char preChar = str1[prePos];
		 while('0' == preChar){
		   str1[prePos]='9';
		   prePos -= 1;
		   preChar = str1[prePos];
		 }
		 str1[prePos] -= 1;
	  }
	  result.insert(0,num_to_string(c));
   }
   return result;
}
string stringFollowZero(string str,int s){
   for(int i = 0; i < s; i++)
	   str.insert(str.size(),"0");
   return str;
}
string IntMult(string x,string y){
   while('0' == x[0] && x.size() > 1){
      x = x.substr(1,x.size()-1);
   }
   while('0' == y[0]&&y.size() > 1){
      y = y.substr(1,y.size()-1);
   }
   int f = 4;
   if(x.size() > 2 || y.size() > 2){
      if(x.size() >= y.size()){
	     while(x.size() > f){
		   f *= 2;
		 }
		 if(x.size() != f){
		    x = stringBeforeZero(x,f-x.size());
			y = stringBeforeZero(y,f-y.size());
		 }
	  }else{
	    while(y.size() > f){
		  f *= 2;
		}
        if(y.size() != f){
		  x = stringBeforeZero(x,f-x.size());
		  y = stringBeforeZero(y,f-y.size());
		}
	  }
   }
   if(1 == x.size()){
     x = stringBeforeZero(x,1);
   }
   if(1 == y.size()){
     y = stringBeforeZero(y,1);
   }
   if(x.size() > y.size()){
     y = stringBeforeZero(y,x.size()-y.size());
   }
   if(x.size() < y.size()){
     x = stringBeforeZero(x,y.size() - x.size());
   }
   int s = x.size();
   string a1,a0,b1,b0;
   if(s > 1){
     a1 = x.substr(0,s/2);
	 a0 = x.substr(s/2,s-1);
	 b1 = y.substr(0,s/2);
	 b0 = y.substr(s/2,s-1);
   }
   string result;
   if(s == 2){
     int na = string_to_num(a1);
	 int nb = string_to_num(a0);
	 int nc = string_to_num(b1);
	 int nd = string_to_num(b0);
	 result = num_to_string((na*10+nb)*(nc*10+nd));
   }
   else{
     string c2 = IntMult(a1,b1);
	 string c0 = IntMult(a0,b0);
	 string c1_1 = stringAddstring(a1,a0);
	 string c1_2 = stringAddstring(b1,b0);
	 string c1_3 = IntMult(c1_1,c1_2);
	 string c1_4 = stringAddstring(c2,c0);
	 string c1 = stringSubtractstring(c1_3,c1_4);
	 string s1 = stringFollowZero(c1,s/2);
	 string s2 = stringFollowZero(c2,s);
	 result = stringAddstring(stringAddstring(s2,s1),c0);
   }
   return result;
}
int main(){
 int f = 1;
   while(1 == f){
   string A,B,C,D;
   string num1,num2;
   string r;
   cout<<"大整数乘法运算（分治法):"<<endl;
   cout<<"输入第一个大整数:";
   cin >> num1;
   int i = 0;
   for(i = 0; i < num1.size(); i++){
      if(num1[i] < '0' || num1[i] > '9'){
	    cout << "您输入的数据不合法，请重新输入：";
		cin >> num1;
		i = -1;
	  }
   }
   cout << "请输入第二个大整数：";
   cin >> num2;
   for(i = 0; i < num2.size(); i++){
     if(num2[i] < '0' || num2[i] > '9'){
	   cout << "您输入的数据不合法，请重新输入：";
	   cin >> num2;
	   i = -1;
	 }
   }
   r = IntMult(num1,num2);
   while('0' == r[0] && r.size() > 1){
      r = r.substr(1,r.size() - 1);
   }
   cout << "结果："<<endl;
   cout << r << endl;
   }
}