【高精度】加法天才

#include <iostream>
#include <string>
using namespace std;
string add(string a,string b){
    if(a.size()<b.size()){
        string temp=a;
        a=b;
        b=temp;
    }
    int len1=a.size(),len2=b.size(),flag=0,pa,pb,sum;
    while(len1>0){
        pa=a[len1-1]-‘0‘;
        pb=len2>0?b[len2-1]-‘0‘:0;
        sum=pa+pb+flag;
        a[len1-1]=‘0‘+sum%10;
        flag=sum/10;
        len1--;len2--;
    }
    if(flag)a="1"+a;
    return a;
}
int main(){
    string a,b;
    cin>>a>>b;
    cout<<add(a,b)<<endl;
    return 0;
}