PAT c++出现两个段错误是什么原因？

Question

测试数据没问题，应该是达到题目要求了。但是有两个段错误需求解？

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include<iostream>

include<string>

include<vector>

include <functional>

include <iterator>

include <algorithm>

include<stdio.h>

include<cmath>

include<ctime>

using namespace std;

int main()
{

vector<int > vec;
int i;
cin>>i;
while(cin.get()!='\n')
{
    vec.push_back(i);
    cin>>i;
}
vec.push_back(i);

if(vec.size()%2!=0)
    vec.push_back(0);

int i1,i2;
auto it=vec.begin();
vector<int> vec1;
while(it!=vec.end())
{
    i1=*it++;
    i2=*it++;
    if(i2==0)
        break;
    vec1.push_back(i1*i2);
    vec1.push_back(i2-1);

}
copy(vec1.begin(),vec1.end()-1,ostream_iterator<int,char>(cout," "));
cout<<*(vec1.end()-1);

system("pause");

}