一道ACM题，总是提示我答案错误

Question

#include
using namespace std;
int change(int a,int b)
{
int ans[100];
int c;
int i=0;
while(a!=0)
{
i++;
c=a%10;
a=a/10;
ans[i]=c;
}
int sum=ans[i];
for(int j=i-1;j>0;j--)
{
sum=sum*b+ans[i];
}
return sum;
}
int main()
{
int ncase;
while(cin>>ncase)
{
int a,b;

    char ch;

    long long sum=0;

    while(ncase--)

    {

        cin>>a>>ch>>b>>ch;

        sum=sum+change(a, b);

    }

    cout<<sum<<endl;
}
return 0;

}

Answer 1