两个超大数相加 C++代码

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转载自http://hi.baidu.com/liuflin/blog/item/207e7ceffdefae11fcfa3cd0.html

#include <iostream>
#include <string>
using namespace std;
class ds
{
public:
void equal(string x,string y,int n1,int n2);
void nequal(string x,string y,int n1,int n2);
private :
string s1,s2;
};
void ds::equal (string s1,string s2,int n1,int n2)
{//两个字符串一样长的时候；
int flag =0;
int i;
int sum =0;
int k = 0;
int add[1000];
for(i=0;i<n1;i++)
{
   sum = (s1[n1-1-i]-48)+(s2[n1-1-i]-48)+flag;
   if (sum >= 10)
   {
    sum -= 10;
    flag = 1;
   }
   else
    flag = 0;
   add[i] = sum;
}
if(flag==1)
   add[i++] = flag;//最后加上一位进位；
for (i--;i>=0;i--)
   cout <<add[i];
}
void ds::nequal(string s1,string s2,int n1,int n2)
{//两个字符串不一样长的时候；
int flag = 0;
int i;
int sum = 0;
int k = 0;
int add[1000];

if (n1 < n2)
{
   for(i=0;i<n1;i++)
        {
    sum = (s1[n1-1-i]-48)+(s2[n2-1-i]-48)+flag;
    if (sum >= 10)
            {
     sum -= 10;
     flag = 1;
            }
    else
              flag = 0;
           add[i] = sum;
        }
        for(;i<n2;i++)
        {
    sum = s2[n2-1-i]-48 + flag;
            if (sum >= 10)
            {
     sum=0;
     flag = 1;
            }
    else
     flag=0;
    add[i]=sum;
        }
   if(flag==1)
    add[i++] = flag;//最后加上一位进位；
   for (i--;i>=0;i--)
    cout <<add[i];
   cout<<endl;
}
if (n2 < n1)
{
   for(i=0;i<n2;i++)
        {
    sum = (s2[n2-1-i]-48)+(s1[n1-1-i]-48)+flag;
            if (sum >= 10)
            {
     sum -= 10;
     flag = 1;
            }
            else
              flag = 0;
            add[i] = sum;
        }
        for(;i<n1;i++)
        {
    sum = s1[n1-1-i]-48 + flag;
            if (sum >= 10)
            {
     sum=0;
                flag = 1;
            }
    else
     flag=0;
    add[i]=sum;
        }
   if(flag==1)
      add[i++] = flag;//最后加上一位进位；
         for (i--;i>=0;i--)
    cout <<add[i];
         cout<<endl;
}
}

int main()
{
ds dashu;
string x1,x2;
cout<<"please input two word:" <<endl;
cin >>x1>>x2;
int n1=x1.length();
int n2=x2.length();
if (n1==n2)
dashu.equal(x1,x2,n1,n2);
else
dashu.nequal(x1,x2,n1,n2);
cout <<endl;
return 0;
}