大整数加法（函数）

#include <iostream>
using namespace std;
string sum(string s1,string s2){  
	if(s1.length()<s2.length()){  
        string temp=s1;  
        s1=s2;  
        s2=temp;  
    }  
    int i,j;  
    for(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;  
}

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