大数相加 模板

#include<iostream>
#include<string>
using namespace std;
int main()
{
string sum(string s1,string s2);
string s1,s2;
cin>>s1>>s2;
cout<<sum(s1,s2)<<endl;
return 0;
}
string sum(string s1,string s2)
{
if(s1.length()<s2.length())
{
string temp=s1;
s1=s2;
s2=temp;
}
for(int i=s1.length()-1,j=s2.length ()-1;i>=0;i--,j--)
{
s1[i]=char(s1[i]+(j>=0?s2[j]-'0':0));
if(s1[i]-'0'>=10)
{
s1[i]=char((s1[i]-'0')%10+'0');
if(i)
s1[i-1]++;
else
s1='1'+s1;
}
}
return s1;
}