Big mod

Code:
#include<iostream>
using namespace std;
int main()
{
    int mod_num;
    string str;
    while(1){
        cout<<"Enter the Big number: ";
        cin>>str;
        cout<<"Enter the mod number: ";
        cin>>mod_num;
        int temp=0;
        for(int i=0;str[i]!='\0';i++){
            temp*=10;
            temp+=(str[i]-'0');
            temp%=mod_num;
        }cout<<"The mod value of "<<str<<" % "<<mod_num<<" = "<<temp<<endl;
    }
    return 0;
}