各位大神，再帮忙解决一下，我为啥程序运行到一半终止啊


#include <vector>
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(){
    fstream cin("aaa.txt");
    vector<int> v;
    string s1,s2,st;
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>s1>>s2;
        if(s1.size()>s2.size()){
            st=s1;
            s1=s2;
            s2=st;
        }
        if((s1[0]-'0')+(s2[0]-'0')>9)
            v.push_back(((s1[0]-'0')+(s2[0]-'0'))%10);
        else
            v.push_back((s1[0]-'0')+(s2[0]-'0'));
        for(int j=1;j<s1.size();j++){
            v[j]=(s1[j]-'0')+(s2[j]-'0')+((s1[j-1]-'0')+(s2[j-1]-'0'))/10;
        for(int m=s1.size();m<s2.size();m++)
            v[m]=s2[m];
        }
        vector<int>::iterator it=v.begin();
        if(*it==0)
            v.erase(it);
        for(int k=0;k<v.size();k++)
            cout<<v[k]<<endl;
    }
    return 0;
}

没学C++

不懂c++