求助!总是卡最后一个样例,样例输入为9000000000和1000000000

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
vector<int> div(vector<int>&A,int b,int&r)
{ vector<int>C;
 r=0;
 for(int i=A.size()-1;i>=0;i--)
 {	r=r*10+A[i];
 C.push_back(r/b);
 r%=b;
 }
 reverse(C.begin(),C.end());
 while(C.size()>1&&C.back()==0) C.pop_back();
 return C;
}
int main()
{string a;
long long b;
cin>>a>>b;
vector<int>A;
for(int i=a.size()-1;i>=0;i--) A.push_back(a[i]-'0');
int r;
vector<int> C=div(A,b,r);
for(int i=C.size()-1;i>=0;i--)
printf("%d",C[i]);


}