c++ - It gives an error for big values -

i solving simple question of finding nth power of 2.it works lower power of n,but fails when try doing higher powers,also,the question have been asked has % 10^9+7 reduce size. if please tell me going wrong.

#include <cmath> #include <cstdio> #include <vector> #include <iostream> #include <algorithm> using namespace std; long long int pro=1;  long long int func(int n) { if(n!=1) {   pro=pro%1000000007;     pro=(2*func(n-1));  return pro; }  return 1; }  int main() {        pro=1;     long long int n=555555;       long long int x;     if(n!=1)   x=func(n);     else       x=1;      cout<<x<<endl;     }  return 0;   } 

 if(n!=1){    x=func(n);  }else{       x=1; //this incorrect, should return 2.  } 

also

    long long int func(int n)     {       if(n!=1)       {           pro=(2*(func(n-1)%1000000007))%1000000007;          return pro;        }        else return 2;      }